Understanding the performance changes of porous geopolymers under high temperature conditions is helpful to optimize application porous geopolymer in high temperature environments. In this study, fly ash-slag based porous geopolymer materials were subjected to high temperature treatment at 200~800 ℃, and the effects of high temperature on the composition, microstructure and macroscopic properties of porous geopolymers were studied. The results show that the most significant mass loss of fly ash-slag based porous geopolymer occurs below 600 ℃, which is mainly attributed to the evaporation and dehydroxylation of free water and bound water. Above 600 ℃, the mass loss is weakened, mainly corresponding to the decomposition of some carbonate substances. The microstructure of porous geopolymer remains basically stable below 200 ℃, and hot cracking and melting begin to occur above 400 ℃. With the increase of heating temperature, the porosity, pore connectivity and average pore size of porous geopolymer increase continuously, the compressive strength decreases continuously, and the thermal conductivity decreases first and then increases.