VANET is new kind of Ad hoc. It is widely used in ITS (Intelligent Transportation Systems), which has many characteristics as large scale network, fast moving nodes, the frequently changing topological structure and easily divided networks. Therefore, routing protocol design must fully consider of this characteristics with much node information that bring a great challenge to the security of VANET. In this paper, we divide the information type into four categories based on different content, and analyze the security threats in different information type, then summarize the existing security technologies and give the possible research directions.