In order to improve the precision in the simulation of rotor airfoil dynamic stall, a numerical method based on hybrid grid and RANS equations in ALE form is established which is available for analyzing dynamic stall of rotor airfoil in low-speed flow. The low-speed preconditioning method is adopted in the form of conserved variables to solve the problem hard to converge due to the big difference in eigenvalue. Structured grid on the wall is generated using advancing-layer Poisson equation, which possesses better texture and orthogonality. The widely used k-ω SST turbulent model is applied to capture the characteristics of the large separation in the deep stall. The calculation results show that this method can effectively analyze the dynamic stall of rotor airfoil under different Mach numbers, and the convergence accuracy is increased by no less than 2 orders of magnitude. The computational analysis of the flow field characteristics of deep stall with different Mach numbers indicates that the Mach number has obvious regularity influence on the hysteresis characteristic of dynamic stall.