Potash is a major source of potash fertilizer in agriculture. China as a big agricultural nation has a 20% of potash fertilizer demand worldwide, but very poor in China’s potash resource, and 70% depending on import. A stable and rational import price is a vital point in potash fertilizer industry. This paper adopts game theory and benefit-cost analysis to discuss how to reach a purchase contract with rational prices for China’s potash importers, aims to keep a stable development of potash fertilizer industry and to guarantee a sustainable increment of agricultural development and national economy.