During the installation and removal of the support of continuous steel box girder bridge, the internal force of the main girder will change, and the range of internal force change is closely related to the position of the support. However, at present, the position of bridge support is mainly determined by experience, which can not effectively reduce the internal force change of main girder during construction and affect the safety of bridge construction. Based on the matrix displacement method, this paper theoretically analyzes the internal force changes of the main girder with or without support, and puts forward the method to determine the optimal position of the support of the continuous steel box girder bridge. According to the theoretical method, the support position is determined and the finite element model is established. The internal force changes of the key sections of the bridge are calculated by numerical simulation and theoretical analysis respectively. By comparing the calculation results and combining the bending moment diagram of the main girder, it can be concluded that the calculation error of the two methods is less than 6%, which shows that the theoretical method has high accuracy and engineering applicability; The optimal position of the support determined by theoretical method is located near the transition point of positive and negative bending moments. Based on this rule, the position of the support can be preliminarily judged in engineering to improve the efficiency and safety of construction.