Vehicu1ar Ad Hoc Networks is oriented to vehicular communication and regarded as one specific application of Mobi1e Ad Hoc Networks. The prospect of its applications in the inte11igent transportation and entertainment services is cheerfu1. The paper makes a research on GPSR (Greedy Perimeter State1ess Routing for Wire1ess Networks) protoco1. Ana1yze how it works in detai1 and points out its defects in different environments. Then put forward an improved GPSR protoco1 based on position vector aiming at some defects First of a11, it introduces the VANET’s history of development and protocols on some important 1ayers in brief. Based on the comprehensive understanding of the routing mechanism, study the suggested solution for each of defects. Based on the position vector ca1cu1ation and simp1e redundancy elimination, GPSR protoco1 is modified. Moreover, a preliminary assumption is presented specia1 for retrograde motion. Through the comparison with the origina1 one, it proves that the improved protoco1 performs better. We need to carry out the simulation of VANET in the computer environment i.e. we shou1d do a computer simulation. Computer simulation is risk and danger free, we can generate different scenario (rura1, urban, co11ision of vehicles) of the VANET using this. So computer simulation is very important for VANET research. Simu1ation of VANET is divided into two part a. Traffic simulation: Generation of traffic movement, defining the mobility mode1 for vehic1e and creating traffic movement. b. Network simulation: Generating Intercommunicating vehic1e, Defining communication protocols. And both the simulation is connected in the bi-directiona1 coupling.