Based on instantaneous potential energy principle and spline interpolate function, the dynamic equation of flat spherical shell is derived. The spline parameters and their derivatives are taken as state variables, the state equation is established. The spline finite element is used for space domain and the state space method is used for time domain respectively. In addition, a state variable recursive scheme is developed. The main advantages of the present method are that one is not necessary to solve linear equations, second is not to be applied to the technique of uncoupling and reduced order and only the matrix operations are required. Some numerical results are presented to demonstrate the effectiveness and reliability of present method.