Abstract: Coal gangue has the characteristics of complex physical and chemical properties, low strength, loose and porous, which limit its extensive use in building materials. In this paper, coal gangue was modified by soaking in hydrophobic solution under uncalcining and non-prewetting conditions. The basic characteristics of coal gangue before and after modification was systematically studied, and hydrophobically modified coal gangue mass substitution rates of 0%, 30%, 50%, 70% and 100% were set. Contact angel, flexural strength, compressive strength, electric flux were used as characteristic parameters to evaluate the influence of modified coal gangue replacement rate on the basic properties of mortar under different substitution rates.Results showed that, by using the binary cooperative complementary method, when the replacement rate of modified coal gangue was lss than 50%, the hydrophobic state of the surface of coal gangue mortar could be achieved. As the replacement rate of modified coal gangue increases, the compressive strength showed a decreasing trend, the maximum decrease was 15.7% compared with none modified coal gangue added. The 28 d compressive strength was 58.5 MPa with 30% replacement rate of modified coal gangue. The electric flux was less than 250 C under different modified coal gangue replacement rate, which indicated excellent resistance to chloride permeability. When the modified coal gangue replacement rate is 30%, the electric flux was the smallest (130 C). The hydrophobic modification method could ensure good mechanical strength and resistance to chloride penetration under the condition of uncalcined and non-prewetted coal gangue, which fully utilizes coal gangue.