Objective To observe the influence of different treatment intervals of pulsed dye laser (PDL) in treating hypertrophic scar after burn, and to explore the optimal treatment interval. Methods From May 2018 to March 2019, 20 burn patients who met the inclusion criteria and were admitted to the First Affiliated Hospital of Air Force Medical University were included in this prospective randomized controlled study. Patients were divided into 1 week group (4 patients, 2 males and 2 females, aged 27 (4, 67) years, 19 scars), 2 weeks group (5 patients, 2 males and 3 females, aged 9 (3, 55) years, 15 scars), 3 weeks group (5 patients, 4 males and 1 female, aged 26 (19, 45) years, 15 scars), and 4 weeks group (6 patients, 4 males and 2 females, aged 31 (14, 48) years, 13 scars), according to the random number table, and treated with PDL with the treatment intervals of 1 week, 2 weeks, 3 weeks, and 4 weeks, respectively, with total treatment cycle of 3 months. Before the first treatment and three months after the first treatment, the Vancouver Scar Scale (VSS) was conducted and the decreased value of VSS score was calculated; the laser Doppler blood flow meter was used to measure scar blood perfusion and the proportion of change in blood perfusion volume was calculated. Data were statistically analyzed with Kruskal-Wallis test, Wilcoxon rank sum test, Wilcoxon symbolic rank sum test, Bonferroni correction, and Fisher′s exact probability test. Results The VSS scores of patients in 1 week group, 2 weeks group, 3 weeks group, and 4 weeks group in three months after the first treatment were significantly lower than those before the first treatment (

=-3.74, -3.47, -2.69, -3.25,

<0.01). There were no statistically significant differences in the decreased values of VSS scores in three months after the first treatment among the patients in 4 groups (

=2.35,

>0.05). Three months after the first treatment, the blood perfusion volumes of patients in 2 weeks group and 3 weeks group were significantly lower than those before the first treatment (

=-2.95, -2.50,

<0.05 or

<0.01). The proportions of changes in blood perfusion volume of patients in 1 week group, 2 weeks group, 3 weeks group, and 4 weeks group were respectively -0.02 (-1.05, 0.69), -0.29 (-0.75, 0.18), -0.11 (-0.55, 0.23), 0.05 (-0.61, 0.75). There were statistically significant differences among the 4 groups (

=9.39,

<0.05). The proportions of changes in blood perfusion volume of patients in 2 weeks group was statistically higher than that of 1 week group (

=2.76,

<0.01). Conclusions PDL treatment can reduce the VSS score and blood perfusion volume of scar. One treatment every two weeks or three weeks improve the scar blood perfusion volume more significantly, and can be recommended as the appropriate treatment interval of PDL for hypertrophic scar after burn.