Today's software is required to be more trustworthy due to its ever more important role in the society. However there is still lack of systematic and objective criteria for the evaluation of software trustworthiness. Existing research focuses on how to get the evidence, with the assumption that system is more trustworthy if the evidence is obtained from a third party test, or from the feedback of past users. Although such study contributes to the objectivity of trustworthiness, the process-oriented nature of system trust is not well addressed. In this case, the sufficiency and necessity of software process related evidence, as well as the coverage ratio of the necessary development process, are critical. This paper attempts to establish the confidence of software product from the trustworthiness of development process. Based on the software development process, software trustworthiness is determined by three aspects:process entity, behavior and products. A software process trustworthiness model is proposed that includes 37 trustworthiness principles, 182 process entities and behaviors evidences, and 108 artifacts evidences. Based on this model, an evaluation method for process trustworthiness is also developed.