Electric vehicles are increasingly flooding into smart microgrid as a kind of mobile distributed energy storage device. To reduce the system cost of the smart microgrid that includes electric vehicles, an online energy scheduling algorithm was proposed by using Lyapunov optimization method. Firstly, a microgrid system with electric vehicles, Combined Heat and Power (CHP) devices and renewable energy source collection devices was constructed. The long-term average cost minimization problem was formulated by considering the mobility and battery loss of electric vehicles, the real-time electricity price of the external power grid and the user demand, which combined electricity demand and heat demand. Then, an online energy scheduling algorithm was proposed by utilizing Lyapunov optimization method to solve the problem. Finally, simulation results on Matlab show that the system cost of the proposed algorithm can reduce 61.79% compared with greedy algorithm when the number of electric vehicles is more than 60.