The T-tail configuration in civil aircraft can reduce downwash and speed inhibition at the horizontal tail, and has higher efficiency. However, this configuration also leads to can constitute a serious asymmetric load situation on the vertical tail. This paper proposes a theoretical calculation formula for the horizontal tail lift under sideslip conditions about T-tail aircraft, obtaining an equation describing the variation of the horizontal tail lift with sideslip angle. Subsequently, the CFD method is employed to simulate and analyze the asymmetric load on the T-tail under crossflow, verifying the accuracy of the proposed calculation formula. Furthermore, by combining the theoretical calculation equation with the results of CFD flow field simulation of the whole aircraft, the impact of different variables on the asymmetric load of the T-tail is determined, providing a basis for the design of asymmetric load for T-tail aircraft.