Reynolds number is one of the most useful similarity parameters in fluid dynamics which denotes the effect of the viscosity on the fluid flow, it has the important effect on the aerodynamic characteristic of the aircraft. The variable Reynolds number research of the high lift for one of the civil turboprop aircraft is completed by the commercial software CFX in this paper. The effect of Reynolds number on the lift coefficient, pressure distribution, stall characteristic, and the velocity characteristic of the boundary layer are also carefully analyzed. The research indicates that the Reynolds number has the notable effect on the maximum lift coefficient and the stall angle; the state of separation on the wing change obviously under the different Reynolds number, the area of separation become smaller when the Reynolds number increases; the state of the boundary layer is different under the different Reynolds number, when the Reynolds number increases, the velocity profile is fuller, the trend of separation is limited.