Abstract: The formation process of a hollow NH4H2PO4 microsphere is firstly mathematically simulated according to its formation process, formation conditions and formation mechanism. Its mathematical model includes continuity equation, momentum equation, energy equation, mass diffusion equation and mass conservation equation. It also takes into account the variation of bubble radius, gas pressure in the bubble, temperature of hollow microsphere and water content distribution during its formation process, under variational density, variational viscosity，mobile boundary and nonisothermal surroundings. In addition, it considers the effect of CMC and surface tension on the bubble radius. The final simulated bubble radius is close to the experimental value.