In recent years, the wireless communication technology rapidly develops and the mobile devices are in widespread used. The IETF Mobile IP working group has proposed the Mobile IP to support IP mobility, and it keeps a session connected when a mobile node roams from subnet to subnet. Novel network type is the mobile ad hoc network (MANET) which is formed by a set of mobile devices with limited power and using multi-hop communication capabilities without through any infrastructure. In order to move to an all-IP environment, we use Mobile IP to provide global Internet connectivity for ad hoc networks. However, the security problems are seemed more and more important. We must avoid routing packet attacks such as packet forgery attack and packet modification attack. In addition, we also must consider the authentication problem. Before using the resource, the mobile node must be verified whether legally or not. In this work, we will propose an efficient authentication mechanism in Mobile IP, and secure routing protocol in MANET. Finally, we propose an authentication mechanism in MANET which is aided with Mobile IP. And we can achieve the security routing and verify the user.