Abstract: The effects of three different types of surfactants, SDS, CTAC and APG, on the surface tension and contact angle of phosphate binder, the fluidity and filling ability of molding sand, and the flexural strength and tensile strength of hot-box molding sand were investigated. The mechanism was analyzed by TEM. The results show that the surfactant reduces the surface tension and contact angle of the binder in different degree, and improves the fluidity and filling ability of the molding sand; when the mass fraction of SDS is 0.2wt%, the filling ability increases by 31.86%, the bending strength decreases by only 2.2%, and the tensile strength decreases.