In future, the main cause of competitive advantage for companies is successful new product development. In recent 30 years, many researches have done about efficiency of NPD process and many various models have been developed to systematize these processes. In the NPD process, great amount of organizational knowledge will be created, stored, retrieved and used. Therefore, many researchers presumed NPD as a high knowledge based process and believe knowledge management system has important role in decreasing uncertainty and increasing success of NPD. In this research, the role of knowledge management and critical success factors have been surveyed in performance of NPD process in software SMEs of Yazd province. The type of this survey is correlation and data were gathered by questionnaire for 43 companies as our society. The results indicated that three research hypotheses were confirmed. Finally, suggestions on the basis of the findings will be presented.