At present, the design of wind-solar hybrid power supply systems is based on personal experiences which could cause a deficient or excess in installed generation capacity. The design of standalone wind-solar hybrid power supply systems could be taken as a multi-objective optimization problem whose two objectives are maximizing systems' reliability and minimizing cost. The power supply reliability is guaranteed by checking a single year's battery's SOC which is mimicked by computer software, and the minimal cost for designing a wind-solar hybrid power supply system is searched by a dynamic GA. Combing with the concrete construction of Yangzhou smart grid state detection, the successful application of wind-solar hybrid power supply systems technology is introduced in detail.