Airfoil stall and its boundary layer development are fundamental scientific issues in aircraft design. For the trailing edge stall airfoil, The transition model coupled the Mentor k-ω SST model with the disturbance amplification factor transport equation is used to analyze the influence of Reynolds number variation on the laminar-turbulent transition boundary layer characteristics and stall characteristics. The results show that when the Reynolds number increases, the local vorticity Reynolds number increases, the transition position moves forward and the separation bubble decreases, the flow energy dissipation decreases, and the overall surface shear effect of the airfoil increases. The kinetic energy is more abundant, the flow self-sustaining ability is enhanced, and the pressure distribution can maintain the gradient resistance of the longer distance to enhance the separation ability; Therefore, the increase of the Reynolds number increases the airfoil stall angle and the lift coefficient.