Web applications are widely used in people's everyday life and are inherent interactive applications since their emergence. The structures of web applications are complex. Furthermore, the interaction features exacerbate their complexity. How to ensure their reliability and quality presents a challenge to software testers. In this paper, according to the features of web applications, we have formally defined and presented intra-page interactions coverage criteria, inter-page interactions coverage criteria, page-server interactions coverage criteria and scenario-based page-server interactions coverage criteria. Based on each of these coverage criteria, using a motivating example, we present a method to generate test sequences. We also give out the discussions on how to choose the corresponding coverage criteria to satisfy software requirements.