Microbial foaming agent was prepared by using yeast, and its foaming mechanism was revealed. Then foam concrete was prepared by mixed mixing method and prefabricated bubble mixing method based on different foaming mechanisms. Effects of different mixing process on the physical and mechanical properties and microstructure of foam concrete were investigated. The results show that microbial foaming agent can not only produce CO2 by yeast fermentation to form foam, but also can reduce the surface tension of foaming agent solution and introduce air foaming under external force by biochemical reaction of yeast. The dry density of foam concrete prepared by mixed mixing method is 1560kg/m3, and the compressive strength is 33MPa, the pore size distribution of the sample is uniform and the equivalent pore size is relatively small to be 880μm, and the calcium hydroxide(CH) from hydration of cement reacts with the CO2 produced by yeast forms a large amount of CaCO3, which leads to the compressive strength of the formed sample being far lower than the requirements of the industry standard. The dry density of foam concrete prepared by premixed foam mixing method is 420kg/m3, and the compressive strength is 11MPa, the pore size distribution of the sample is not uniform and the equivalent pore size is relatively large, which is 1080μm, at the same time, a large amount of calcium silicate hydrate（C S H）is contained in the sample, with the result that the compressive strength is much higher than the industry standard.