Objective: To explore the cutting scheme and clinical application effects of ultrathin thoracodorsal artery perforator flap assisted by color Doppler ultrasound. Methods: This study was a retrospective historical control study. From February 2017 to October 2019, 20 patients who were admitted to the Third Department of Orthopedics of Xingtai General Hospital of North China Medical and Health Group (hereinafter referred to as our department), met the inclusion criteria, and underwent repair of skin and soft tissue defects of extremities with ultrathin thoracodorsal artery perforator flap designed and harvested based on the surgeon's clinical experience were selected as control group, including 16 males and 4 females, aged (37±5) years. From November 2019 to December 2022, 21 patients who were admitted to our department, met the inclusion criteria, and underwent repair of skin and soft tissue defects of extremities with ultrathin thoracodorsal artery perforator flap designed and harvested under the assistance of color Doppler ultrasound were selected as ultrasound-assisted group, including 15 males and 6 females, aged (38±6) years. After debridement, the area of skin and soft tissue defects of extremities ranged 5.0 cm×4.0 cm to 19.0 cm×8.0 cm, and the area of thoracodorsal artery perforator flaps ranged 6.0 cm×5.0 cm to 20.0 cm×9.0 cm. The wounds in flap donor sites were closed directly. For patients in ultrasound-assisted group, the time and cost required for color Doppler ultrasound examination were recorded, and the number, type, and location of thoracodorsal artery perforator vessels detected by preoperative color Doppler ultrasound were compared with those of intraoperative actual detection. The time required for complete flap harvest of patients in 2 groups was recorded. On postoperative day (POD) 1, 3, 5, 7, and 14, the blood perfusion of flaps in the 2 groups of patients was assessed using a flap perfusion assessment scale. On POD 14, flap survival of patients in 2 groups was observed, and the percentage of flap survival area was calculated. In postoperative 6 months, satisfaction of patients with the treatment outcome in the 2 groups was assessed using 5-grade Likert scale, and the satisfaction rate was calculated. Results: For patients in ultrasound-assisted group, the time required for preoperative color Doppler ultrasound examination was (10.5±2.3) min, and the cost was 120 yuan; 21 thoracodorsal artery perforator vessels were detected and marked using preoperative color Doppler ultrasound, including 8 (38.10%) type 1 perforator vessels, 10 (47.62%) type 2 perforator vessels, and 3 (14.29%) type 3 perforator vessels; the number, type, and location of thoracodorsal artery perforator vessels detected preoperatively were consistent with those detected intraoperatively. The time required for complete flap harvest of patients in ultrasound-assisted group was (41±10) min, which was significantly shorter than (63±12) min in control group (t=6.32, P<0.05). On POD 1, 3, 5, 7, and 14, the blood perfusion scores of flaps of patients in ultrasound-assisted group were significantly better than those in control group (with t values of 6.67, 7.48, 8.03, 8.75, and 7.99, respectively P<0.05). On POD 14, only one patient in ultrasound-assisted group had partial flap necrosis and 6 patients in control group had complete or partial necrosis of the flap; the percentage of flap survival area of patients in ultrasound-assisted group was (99±8)%, which was significantly higher than (87±8)% in control group (t=4.57, P<0.05). In postoperative 6 months, there was no significant difference in the satisfaction rate of patients with the treatment outcome between the two groups (P>0.05). Conclusions: Preoperative color Doppler ultrasound is highly accurate in detecting the number, type, and location of perforator vessels. The cutting scheme of ultrathin thoracodorsal artery perforator flaps can be designed according to the different types of perforator vessels, with shorted flap cutting time and improved flap survival rate.