Abstract: The government emergency materials reserve is the supporting power for emergency management material, the current researches mostly are concerned with material reserves——how to become more effectively in serving the emergency work, rarely consider the reserve the cost issue. Within the limited funds of the government, minimizing the cost of the reserve is a part of improving the whole efficiency of emergency management. According to the emergency material's essential characteristics, and depending on the existing reserve methods, they are physical reserves, productivity reserves, and contracts reserves. This paper will summarize it into two modes——physical reserves and emergency purchase reserves. Through analyzing these two categories of the reserve modes, especially analysis of the substitution and complementary relationship between them, it is easy to find that the substitution between the two species is incomplete. Based on the full consideration of financial funds, what kind of level the quantity of the government emergency material storage should be kept in which will neither delay the emergency nor make the highest cost? By the concrete analysis, a critical point is found between physical reserves and emergency purchase reserves from the substitution to complementary relationship interval, which determines optimal reserves, and this quantity can meet the prerequisite of providing emergency materials support level unchanged under the minimum cost of material reserve, thus achieving the purpose of optimization of the use of emergency funds.