In order to promote the high value-added utilization of high calcium fly ash, the geopolymer with excellent mechanical properties was prepared using fly ash as main raw material by water glass alkali excitation. Then, hydrogen peroxide was introduced as foaming agent, sodium dodecyl sulfate (SDS) was used as foaming stabilizer and the foaming process was optimized to prepare porous foaming geopolymer. The pore size distribution of foaming section was analyzed by Image-Pro Plus image software and the microstructure of foaming geopolymer was characterized by XRD, FTIR and SEM-EDS. The results show that under the conditions of liquid-solid ratio of 0.50, alkali equivalent of 10% (mass fraction), water glass modulus of 1.50, H2O2 content of 3% (mass fraction), SDS content of 0.3% (mass fraction) and foaming at 80 ℃ for 4 h, the 28 d compressive strength of specimen after standard curing is 1.78 MPa, and the apparent density is 631 kg/m3. Foaming geopolymer has small pore size and uniform distribution, resulting in low density. The polymerization product is a small amount of C-S-H gel and a large amount of N(C)-A-S-H gel produced by the synergistic reaction of calcium, aluminum and sodium, which ensures the mechanical strength of foaming geopolymer.