Objective To explore the methods and effects of high-frequency color Doppler ultrasound assisted reverse island flap of dorsal digital artery of ulnar thumb for repairing skin and soft tissue defects in the distal end of the same finger. Methods The retrospective cohort study method was applied. From March 2014 to January 2020, 43 patients with skin and soft tissue defects in the distal end of thumb were hospitalized in the Department of Hand and Foot Surgery of Yidu Central Hospital of Weifang, including 28 males and 15 females, aged 19-58 years. The time from injury to operation was 4 to 10 hours, and the area of wound defect was 1.5 cm×1.0 cm-5.0 cm×3.0 cm. The type and course of dorsal digital artery of ulnar thumb were detected by high-frequency color Doppler ultrasound before operation, based on which the reverse transfer of the island flap of dorsal digital artery of ulnar thumb was designed to repair the skin and soft tissue defects in the distal end of the same finger. The patients with absence of the dorsal digital artery of ulnar thumb were repaired by the greater fish reverse island flap pedicled with the radial palmar artery. The area of the flap was 2.0 cm×1.5 cm-5.5 cm×3.5 cm. The donor site wound was directly closed by suturing or covered with split-thickness skin graft from the inner side of the upper arm in the same arm. The status of dorsal digital artery of ulnar thumb detected by high frequency color Doppler ultrasound before operation was recorded. The type, course, and distribution of the dorsal digital artery of ulnar thumb detected before operation were compared with those observed during the operation. The survival of the flap was observed after operation. During the last follow-up, the appearance of the donor and recipient area of flaps was observed, the thumb function was evaluated with trial standard for the evaluation of the functions of the upper limbs of the Hand Surgery Society of the Chinese Medical Association, and the sensory function of the area transplanted with flap was evaluated with the sensory function evaluation standard. Results The results of high-frequency color Doppler ultrasound showed that the dorsal digital artery of ulnar thumb was absent in 2 patients, while 41 patients had the dorsal digital artery of ulnar thumb, among which 20 cases were type 1 that started from the first dorsal metacarpal artery and ran on the surface of the first interosseous dorsal muscle; 16 cases were type 2 that started from the deep branch of the radial artery or the main artery of thumb and ran in the deep surface of the first interosseous dorsal muscle, including 10 cases of type 2a with the starting point in the basal region of the first metacarpal bone and 6 cases of type 2b with the starting point in the first metacarpal bone region; 5 cases were type 3 that started from the confluence of the first dorsal metacarpal artery and the main thumb artery in the region of the first metacarpophalangeal joint. The outer diameter of the vessel at the beginning of the dorsal digital artery of ulnar thumb was (1.12±0.31) mm, and the outer diameter of the vessel at the beginning of the accompany vein was (0.63±0.21) mm. The dorsal digital artery of ulnar thumb was concentrated in the ulnar side of the first metacarpophalangeal joint and snuff box region. The type, course, and distribution range of the dorsal digital artery of ulnar thumb observed during the operation were consistent with the results detected by high-frequency color Doppler ultrasound before operation. After the operation, the flaps survived in 43 patients. The patients were followed up for 6 months to 1 year. During the last follow-up, only linear scars were left in the donor area; there were no obvious pigmentation in the area transplanted with reverse island flap of dorsal digital artery of ulnar thumb, with good texture and elasticity, and beautiful appearance; the thumb function was evaluated as excellent in 23 cases, good in 17 cases, and fair in 3 cases; the sensory function of the area transplanted with flap was evaluated as S₄ level in 16 cases, S₃ level in 22 cases, and S₂ level in 5 cases. Conclusions The reverse island flap of dorsal digital artery of ulnar thumb is one of the ideal methods to repair the skin and soft tissue defect in the distal end of the same finger, especially that beyond the distal interphalangeal joint. Preoperative detection with high-frequency color Doppler ultrasound can identify the type and distribution of dorsal digital artery of ulnar thumb, so as to design a personalized operation plan, resulting in good appearance of the donor and recipient area and thumb function after operation.