Potassium hydroxide was used to adjust the modulus of sodium water glass to prepare compound alkali activator. Taking sodium water glass modulus and alkali content as variables, the effect of potassium hydroxide on sodium water glass activated slag cementitious material performance was analyzed, and the change law of fluidity, setting time and compressive strength of potassium hydroxide-sodium water glass activated slag cementitious material was studied. The results show that the stimulating effects of potassium hydroxide-sodium water glass compound alkali activator are better than those of single sodium water glass activator. When the sodium water glass modulus is 1.2 and the alkali content is 8% (mass fraction), the fluidity of potassium hydroxide-sodium water glass activated slag cementitious materials reaches up to 240 mm, and the compressive strength of 7 d and 28 d reaches up to 98.88 MPa and 104.59 MPa, which is 16.7% and 22.9% higher than that of the sodium water glass activated slag cementitious materials under the same conditions.