In view of the shortcoming of the existing structural reliability calculation method, this paper establishes optimization model of the structural reliability index from the geometric meaning of the structural reliability index. Then, the authors propose a method based on improved particle swarm optimization algorithm for solving the reliability method. Particle swarm algorithm is easy to fall into local optimum. So, the authors construct simulated annealing particle swarm algorithm which has the strong local search ability .simulated annealing particle swarm algorithm is a global optimization algorithm. Using it to solve the reliability index can avoid doing partial derivatives to the structural performance function and the deficiency of traditional method is effectively overcomed which is easily being trapped in local optima. Therefore, it is a very effective method to solving the structural reliability index of the complex structure. In the end, some examples demonstrate the validity of this method.