With the rapid development of smart grid, the large scale vehicle-to-grid (V2G) electric vehicles (EVs) will been widely applied. However, the interaction between EVs and the power grid will bring many challenges. In order to lighten the adverse influence on the grid operation, the regional EV load should be estimated in advance. By thoroughly considering the impact factors of regional EV load on the gird, this paper presents a methodology to determine the regional EV load. Monte Carol simulation algorithm is adopted to draw the random numbers of impact factors and to achieve the simulation of EV load curve. Three kinds of EV load models are built and simulated including uncontrolled charging model, controlled charging model and controlled charging/discharging model. The impact of three different EV load models on the grid load curve and on the load rate and peak-valley difference of the grid is given in this paper. And the impact of different scale of EVs on the grid is also discussed. The EVs in Qingdao Economic and Technological Development Zone (QETDZ) in Qingdao city, Shandong Province, China are taken as an example to analyze the impact on the grid of different regional EV load models. The simulation results show that the three EV load models built in this paper are helpful to study the impact on the power grid and have a potential value in practical applications.