In order to improve the emergency response ability of flood disasters, a three-agent mixed reserve model of emergency materials is put forward in this paper. Based on the analysis of the supply of the three-agent reserves and the demand of materials, a materials reserve distribution model is established, which aims at the minimum government cost and the lowest disaster loss. The allocation model of materials reserves is restricted by the guarantee capacity of each subject, government cost and enterprise profit. Through the simplification of the model, the applicable scope of different reserve modes is determined. Based on the calculation of the examples of flood emergency materials represented by block stone, the optimal allocation structure under different reserve modes is analyzed and compared, and the sensitivity analysis is carried out for the important parameters related to government decision-making. The conclusions are as follows: for the flood emergency materials represented by block stone, it is suggested that the reserve mode should be based on the direct reserve of the government, supplemented by the reserve of enterprises, and supplemented by the reserve of social forces; the purchase cost of materials in the spot market will affect the total amount of material reserves, thus the purchase and reserve cost of government reserve and the price of enterprise option will affect the material reserve structure.