China's wind and solar energy capacities have increased considerably over the previous decade, and these energy sources are playing increasingly important roles in China's power sector. However, because of their variability and intermittency, increasing the supply of wind and solar energy to the electricity grid is a challenge. In this study, we first assessed the integration cost of wind and solar energy together with the coal efficiency penalty attributable to the intermittency of wind and solar energy. Then, with consideration of the intermittency effect, we investigated the roles of wind and solar energy in China's power sector in terms of their electricity generation, generation share, substitution effect, and emissions reduction under two scenarios: i.e., with and without adoption of climate mitigation policies. Finally, we estimated the impact of intermittency on future deployment of wind and solar energy. The results indicated that by 2050 the shares of wind and solar energy in China's power sector under the two scenarios will decline by more than 10% and by more than 15%, respectively, compared with the case without consideration of intermittency. The results also illustrated that the coal share, grid generation cost, and carbon emissions per unit generation will increase by 0.5-1.1%, 1.2-3.7%, and 1.8-4.1%, respectively. Sensitivity analyses indicated that the change in variable renewable energy (VRE) share would be negatively proportional to the changes in VRE integrated cost and coal efficiency penalty.