Wind power in China is developing rapidly. However, wind power curtailment has become increasingly severe, reaching 15% in 2015. The root cause of wind power curtailment in China is that its power system has insufficient flexibility. We analyze how to achieve a reasonable allocation of ancillary service costs for wind power plants, using a cooperative game approach. The analysis shows that, while the current allocation approach in the Beijing, Tianjin, and Tangshan power grid is based only on wind feed-in tariffs, an allocation method based on both the feed-in tariff and the capacity credit of wind would be more reasonable.