Electric vehicles play an essential role in low carbon development and have significant implications for the power grid. The purpose of this study is to examine the economic value of electric vehicle integrating into the power grid. An electricity supply cost model is established to investigate the cost reduction under three charging operation modes, including random charging, controlled charging, and V2G charging. The results reveal that the adoption of EVs can effectively improve the power grid's load factor and reduce the electricity supply cost. Under the random charging mode, the marginal electricity cost is 556.5 CNY/MWh, which is lower than the grid's power supply cost of 597.1 yuan/MWh. The controlled charging without V2G can further smooth the load curve and drop the power supply cost to be 495.2 CNY/MWh. In the V2G model, the grid revenue is complicated with the consideration of battery degradation costs and the optimal total revenue could be 148.4 million CNY. The main policy implication is that the government should deregulate the electricity market and allow electric vehicles to participate in the electricity market as a power source.