This paper focuses on the study of the reliability distribution model of software system architecture and corresponding optimization algorithm based on,creating system of optimum reliability with minimum cost, which not only considers minimizing development costs, but also optimizes the reliability of the software system. In this paper, the proposed model and algorithm for the theory has a certain reference value to reduce software development costs, improve the reliability of software systems, and can evaluate designed software architecture before software development so as to predict the development of software system cost and make an optimal allocation of software reliability, possessing higher practical application value.