Objective To study the effects of selecting different fixing segments on biomechanical characteristics of the spine during the treatment of early onset scoliosis（EOS） by growing rod technique. Methods By using finite element method, four spine models (C6-S1 segments) fixed by growing rod were established: preoperative model, T1-L4 fixed model, T2-L4 fixed model, T3-L4 fixed model. Then 7 N·m torque load and 1 rad angular displacement load were applied on superior surface of C6 segment to analyze biomechanical characteristics for adjacent structure of the fixed vertebral body. Results The whole spinal range of motion (ROM) decreased significantly after operation. When the T2-L4 segment was fixed, the spine activity was mostly restricted, the compensatory activity of adjacent vertebrae increased significantly, and the intervertebral disc stress increased significantly. Conclusions When T2 segment is selected as the upper instrumented segment, the risk of proximal junctional kyphosis and spinal degeneration is the highest, which should be avoided in clinical surgery.