In order to develop highquality software process models,it is necessary to research on the normalization of software process models. Considering the properties of traditional software processes and software evolution processes,this paper puts forward the concepts of 1PNF,2PNF,3PNF and 4PNF,which are based on the formal definition of processes from EPMM. This paper suggests that all traditional software process models should be designed to meet 2PNF,and software evolution process models should be modeled to satisfy 3PNF. This paper is a guide to modeling software process models.