Objective: To modify the sliding bi-pedicled gastrocnemius flap technique, quantify its indications for repairing the composite Achilles tendon defects, and lessen the donor site morbidity. Methods: Thirty adult specimens of the lower extremity were used. The simulations of the bi-pedicaled gastrocnemius flap were made on these specimens with the detachment of the proximal soleus and the preservation of the integrity of Achilles tendon. The sliding distances of this flap were measured under different degrees of knee flexion. Results: When the knees flexed 0 , 30 , 60  and 90 , the average sliding distances of the flap were 13.83mm, 25.00mm, 32.67mm and 39.50mm respectively. Conclusions: The mere detachment of the proximal soleus and preservation of the integrity of Achilles tendon during the sliding of bi-pedicled gastrocnemius flap is applicable anatomically and is suitable for repairing the composite Achilles tendon defects within 40mm.