Abstract: This paper deduced a SaaS software lifecycle model based on roles and their interactions. The elements and basic roles of SaaS software ecosystem were firstly proposed. Secondly, the model of roles and their interactions in SaaS software lifecycle was defined. And thirdly, the optimized interaction path from many simulated paths was selected and adjusted. Then based on the optimized paths, the approach of simulating lifecycle was designed, including the selection of interactions and interacted time. Finally, the phrases of lifecycle by clustering the interactions on timeline were deduced. Theories and experimental results indicated that the proposed approach could properly deduce the SaaS software lifecycle model.