Coal gasification slags can be divided into coarse slag and fine slag, which has potential application in alkali-activation field. The physical and chemical properties of coal gasification coarse slag were studied, and the geopolymer was prepared by using coal gasification coarse slag, meanwhile geopolymer modified by TiO2 was studied. The results show that the mechanical properties of coal gasification coarse slag based geopolymer significantly improve by adding a certain amount of TiO2. When 10.0% (mass fraction) TiO2 is added, the 28 d compressive strength of the sample increases from 23.4 MPa to 42.9 MPa. In addition, through phase and microstructure analysis of the samples, the addition of TiO2 significantly improves the microstructure of the geopolymer, promotes the alkali-activation reaction, and improves the mechanical properties of the material.