This paper summarizes the research of mental state model for agent, which is a major subject in the research on multi-agent system. Most references are published after 1990. From different perspectives, covering informal analysis, formal models, architectures, cooperation researches, and applications, many important results are introduced in this paper, such as Bratman's analysis, Cohen and Levesque's intention model, Rao and Georgeff's BDI model, etc. Finally, some prosperous works are introduced as well. We hope that this presentation can help readers deepen their understanding of agent.