In order to explore the effects of different internal fixation systems on the biomechanical characteristics of the spine after orthopedic idiopathic scoliosis, a theoretical basis for the improvement of the internal fixation system was provided from the perspective of biomechanics. Based on reverse engineering, topology optimization and finite element modeling techniques, the finite element model of idiopathic scoliosis was established by taking actual cases as examples. The personalized fusion device was designed. Two kinds of internal fixation systems were established, namely full fixation and interval fixation. To simulate idiopathic scoliosis surgery and compare the biomechanical differences between spine and internal fixation system under different physiological conditions. The results show that the average stress of cortical bone and cancellous bone is increased by 17.19% and 12.37%, respectively, compared with that of interlocking nails. The maximum equivalent stress of fibrous annulus matrix and nucleus pulposus is increased by 1.78% and 1.1%, respectively, compared with that of full nailing. The maximum equivalent stress of pedicle screws is 11.64% higher than that of interlocking screws. The average stress of interbody fusion is increased by 6.15% compared with that of interbody fusion. In conclusion, compared with the interspaced nailing scheme, the total nailing scheme is better in vertebrae safety, but the risk of screw slip and screw loss is higher. Compared with the total nailing scheme, the interstice nailing scheme has better spinal fusion effect and effectively alleviates stress occlusion, but the incidence of bone hyperplasia is increased.