Ad hoc networks are a new wireless networking paradigm for mobile hosts. In this paper, we designed an intelligent transport system. The ITS (intelligent transport system) includes two big function modules: Information processing application system and Road condition information transferring system. The main task of the road condition information transferring module is in charge of the information exchange of the car inside, car to car and car to road. The module works in ad hoc network, we call the network VANET (vehicular ad-hoc network) . Vehicular networks are likely to become the most relevant form of mobile ad hoc networks. For the sake of insuring the system can run normally, the information can be transferring correctly and fleetly, the security of VANET (vehicular ad-hoc network) of the road condition information transferring system is crucial. So integrate the characteristics of ad hoc network itself, in the ITS of this paper, we concern the security issues of VANETs from some aspects and provide the appropriate solving measures. To make sure the ITS can be used under the security pattern.