In order to maximize the usage of renewable generation, compensate its fluctuation and acquire a continuous and smooth output, this paper defines two indices. Complementary degree is defined for measuring the natural complementary characteristics of the stochastic generations, and smoothness is defined for measuring the effect of manual complementariness between adjustable and stochastic generations. These two indices are employed to study the natural complementary characteristic involving wind power and PV, and the manual complementariness involving wind power, PV and energy storage system, respectively. Finally, analyses of two indices are synthesized to form a complementary strategy. This study is a guidance to determine the ratio of stochastic generations and the capacity configuration of adjustable generations as well as a good reference for optimizing the size of ESS in this site.