A type of vortex generator is designed for a certain type of mountain transport aircraft, which is installed on the lower surface of the horizontal tail to improve the flow pattern of the horizontal tail at a negative angle of attack and delay the negative stall of the horizontal tail. The flow characteristics and mechanism of the horizontal tail airfoil with and without vortex generator are studied by numerical simulation method, the pitching moment characteristics of the airfoil are analyzed, and the flow control effect of the vertex generator is verified; The vortex generator is installed on the lower surface of the horizontal tail from the wing root to the position of 80% wingspan, and the aerodynamic characteristics of the aircraft with and without the vortex generators are compared and analyzed. The calculation results show that the negative stall angle of attack and the pitching moment inflection point of the horizontal tail with the vortex generator is delayed by 4°, and the flight boundary of the aircraft is enlarged.