A three-dimensional model of atomic layer deposition (ALD) reaction chamber was established. The influence of process parameters such as pressure, precursor pulse time and temperature on precursor distribution in ALD process was simulated and analyzed by ANSYS Fluent software. The simulation results show that the lower the reaction pressure is, the higher the diffusion coefficient of Mg(Cp)2 precursor molecule will be. And the longer the precursor pulse time is, the more even the distribution of it in the reaction chamber will be. When the pulse time is 250ms, the distribution of Mg(Cp)2 in the reaction chamber was basically even, and the mass fraction of the precursor in each part of the reaction chamber was basically the same. When the pulse time is 200ms, H2O is basically evenly distributed in the reaction chamber. In the ALD temperature window of MgO film, the diffusion effect of Mg(Cp)2 precursor molecule is stronger with the higher temperature in the reaction chamber.