Objective To study the improved index finger dorsal island flap for primary repair of thumb tip injury. Methods Between January 2009 and February 2010, 23 patients with thumb tip injury were treated. There were 17 males and 6 females, aged 21-47 years (mean, 27.5 years). The causes of injury were mechanical injury in 18 cases and heavy crushing injury in 5 cases. The time from injury to operation was 2.5-5.0 hours (mean, 3.5 hours). The defect locations included ulnar palmar defect in 5 cases, dorsal foot defect in 6 cases, radial palmar defect in 8 cases, and radial dorsal defect in 4 cases. All patients complicated by exposure of the thumb distal phalanx. The wound area varied from 2.1 cm × 1.8 cm to 2.8 cm × 2.5 cm. According to distal soft tissue defect of thumb, a modified index finger dorsal island flap was designed, key point of which was moved forward, and defects were repaired with the flaps. The size of flap was 2.3 cm × 2.0 cm to 3.0 cm × 2.7 cm. The donor sites were repaired with skin graft. Results All the flaps and grafts survived after operation and the wounds healed by first intention. All patients were followed up 6-12 months with an average of 6.4 months. The appearance and texture of the flaps were excellent. At last follow-up, the sensation of the flaps recovered to S3+ in 18 cases, to S3 in 2 cases, and to S2 in 3 cases. The two-point discrimination was 3-4 mm. Thumb opposition function was normal without contracture at the first web space. The skin graft at the donor site survived completely, and the metacarpophalangeal joint at donor site had the flexion and extension function. Conclusion Using a modified index finger dorsal island flap for primary repair thumb tip injury is a simple operation, which has good blood supply and high survival rate. When the pedicle flap rotation point is moved forward 10 mm or more, it can meet the needs of repairing thumb tip defect.