Compared with solar photovoltaic（PV） cells or wind power systems， hybrid PV/wind power supply system is more economical， reliable and adaptable to environmental changes. This paper presents an improved evolution algorithm to solve the optimization of the capacity of PV/ wind hybrid system. While meeting the basic requirements of independent power system， the minimum cost of objective function is constructed considering investment costs and operating costs. According to the evolution condition in the proposed algorithm， a dynamic parameter adjustment mechanism is adopted to enhance its search efficiency; the population overlap is monitored in real time; for overlapped individual， the global optimal searching ability of the proposed algorithm is further improved by use of migrant operation strategy. The method presented proves to be effective by an example.