The output of a virtual power plant（VPP）with wind power and dispatchable plug-in electric vehicles（EVs）included fluctuates as the result of the intermittence of wind power and uncertain number of EVs.Thus，in participating the competition in an electricity market，a VPP must address its output uncertainty.Given this background，the problems of developing a joint optimal bidding strategy for a VPP in the day-ahead spot market and regulation market are examined，with a special focus on the impacts of uncertain factors.Some assumptions are made:（1）the up and low limits of the wind power output are modelled as stochastic variables;（2）the electricity market prices in the day-ahead spot market and regulation market are modeled as stochastic variables with given intervals;（3）the number of EVs is huge，and could mitigate the output intermittence of wind power and at the same time participate the regulation market.Under these assumptions，a joint bidding strategy model for a VPP participating in the day-ahead spot and regulation markets is presented based on the robust optimization theory，with the battery discharging cost and the expected percentage of the bidded reserve capacity dispatched in each bidding period taken into account.Then，the commercial solver CPLEX 12.2 is next used to solve the developed robust optimization model.Finally，a sample example is employed to demonstrate the feasibility and efficiency of the developed model and algorithm.