Abstract: A reasonable system capacity configuration scheme is an important basis for the development and utilization of renewable energy. An optimal capacity configuration method for the grid-connected wind-photovoltaic-pumped-storage joint operation system is proposed. The method establishes a system model with the optimization objectives of the minimum cost, the maximum economic benefit and the minimum carbon emission. Based on the real data of a coastal island in southeast China, the model is solved by fast and elitist non-dominated sorting genetic algorithm-Ⅱ（NSGA-Ⅱ）. Then, grey relational analysis（GRA） is introduced to achieve an unbiased trade-off strategy to obtain the optimal capacity configuration scheme. The results show that the joint operation system can achieve continuous and stable operation on the basis of maximum utilization of wind and solar energy. It is feasible to introduce GRA to determine the optimal capacity configuration scheme, and the carbon emission of the joint operation system in the whole project cycle decreases with the increase of the grey correlation degree. Increasing the access rate of wind and photovoltaic power appropriately can reduce the system cost, improve economic benefits and reduce carbon emission.