Electric vehicle (EV) has a promising future due to its friendliness to the environment and potential to reduce dependence on fossil fuels. If large-scale EVs access to the power grid charging disorderly, it may lead to some problems in power grid, such as power congestion. This will threaten the security and economic operation of power grid. Therefore, a EVs’ charging and discharging optimal scheduling strategy based on bi-layer optimization is proposed:in the transmission system, with the objective of reducing the operation costs and PM2.5 emissions of generators, charging cost of users and wind curtailment of wind farms, the upper layer optimization model is built based on day-ahead unit commitment (UC); in the distribution system, with the goal of reducing the network loss, the lower layer optimization model is built based on OPF considering network constraints and mobility of EVs. Based on a power system model consisting of a 10-unit transmission grid and an IEEE 33-bus distribution grid, the effectiveness and superiority of proposed bi-layer optimization strategy is investigated. This work is supported by National Natural Science Foundation of China (No. 51277135) and Science and Technology Project of Hebei Electric Power Company and Central University Science Foundation (No. 2042015kf1004).