The foam geopolymer was prepared by alkali activation method with fly ash and slag as main raw materials. The effects of alkali activator module and fly ash content on the microstructure， compressive strength and thermal conductivity of foam geopolymer were studied. The internal mechanism of reaction products and pore structure parameters influencing the properties was analyzed based on X-ray diffractometer（XRD）， optical microscope and computed tomography（CT） scanning. At the same time， the correlation between pore structure parameters and thermal conductivity and strength was obtained based on grey correlation analysis. The results show that the thermal conductivity of foamed geopolymer is mainly determined by the porosity of the sample， and they are exponentially negatively correlated. The compressive strength is related to pore connectivity， porosity， average pore size and fractional pore proportion， and the influences of pore connectivity and porosity was the most significant.