Nowadays, SaaS is increasingly used by web-based applications for the benefits and profits it brings to both users and service providers. It is significative if service providers can automatically convert traditional applications into SaaS mode, a SaaSify tool is needed urgently. In this paper, we analyze and conclude the new challenges of automatically SaaSify webbased application, propose several key technologies for SaaSifying, and further propose SaaSify Flow Language (SFL) to model and implement SaaSify process; finally, we use a case study to show the effects of proposed tool, and the performance experiments prove that the proposed approach is efficient and effective.