In this paper, fly ash, slag and carbide slag were used as precursors, and sodium hydroxide and sodium silicate were used as mixed activators to prepare geopolymer. The effects of precursor ratio and activator parameters on the compressive strength of fly ash-slag-carbide slag based geopolymer were investigated, and the microstructure was observed by mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). It is found that the compressive strength of geopolymer increases first and then decreases with the increase of the carbide slag replacing fly ash content, liquid-solid ratio, and activator modulus. When the carbide slag replacing slag content decreases, or the activator concentration increases, the compressive strength increases continuously. Adding carbide slag in the precursors with appropriate amount to replace fly ash positively affects the geopolymer compressive strength. The total porosity and the large pore proportion of geopolymer are generally negatively correlated with the compressive strength. The higher the strength is, the denser the microstructure of geopolymer is. The optimum ratio of geopolymer derived from the test is 32∶15∶3 for the mass ratio of fly ash, slag and carbide slag, 0.55 for the liquid-solid ratio, 30% (mass fraction) for the activator concentration, and 1.2 for the activator modulus, which corresponds to a 28 d compressive strength of 77.83 MPa.