In the evolution of the software development process model, the new problems arising from software development represent one of the driving forces from objective world. It is because that with the proliferation of computers new fields using computer will appear. In new fields, the new problem will come out. At the same time, the objective world is in constantly diversification and new problems will emerge in the field equipped with computers. When developing software, people will find it difficult to cope with new problems with the original model. In order to solve new problems, people need to build new software development process models.