Abstract: The stiffness matrix, damping matrix and massive matirix of a spline box arch segment element are built by thin-walled box girder theory and spline finite point method, considering the charactistics of extension, compression, flexure, torsion, torsional warpage, distorsional warpage and shear lag deflection. The dynamic model for analysis of box arch bridges is built by Qin Rong method, this procedure decomposes three dimensional problem into one dimensional problem. Then the unconditionally stable algorithm for the solving of the dynamic equations is formed by the method of spline weighted residual, which formed a whole new set of method to analyze the seismic response of box arch bridges. With few unknown quantities and less computation time, the numerical results of this new method are in good agreement with an exact solution.