An accurate description of the transition corridor is important for VTOL fixed-wing UAV flight. To study the transitional flight process of vertical take-off and landing fixed-wing UAVs, a transition corridor model of this type of UAV is established in this article. From the perspective of flight dynamics, the deflection angle-speed envelope of the power system is studied with the maximum lift coefficient of the wing and the system available power limit. The influence of the overall parameters and energy parameters of the UAV on the deflection angle-speed envelope of the power system is analyzed, and a method to expand the transition corridor of the vertical take-off and landing fixed-wing UAV is proposed. Through case calculations, the transition flight corridors were obtained, and based on the transition corridor model calculations, it was concluded that increasing the available power by 10% can expand the transition corridor by 21.43%, while increasing the aerodynamic parameters by 10% can only expand the transition corridor by 2.33 %.