With the continuous development of internet technology and the globalization of economy, SMEs are facing great opportunities as well as challenges. On the one hand, SMEs urgently need the introduction of IT systems and services, including accounting information system, to improve efficiency, reduce operational costs and enhance competitiveness. On the other hand, comparing with large enterprises, SMEs are constrained by limitation of capital budget, hardware, software and human resources. As a new model of software application, SaaS develops from ASP model, which began at the end of last century. It will have a profound impact on the model of accounting information system.