During the cruise, the speed response system of permanent magnet synchronous motor (PMSM) in the manned electric aircraft is easily affected by parameter perturbation and external turbulence. In order to solve this problem, an online identification and torque compensation sliding mode control (SMC) method for PMSM of manned electric aircraft is put forward. The rotational inertia is identified online by the adaptive forgetting factor recursive least squares, so as to match the parameters of the controller in real time. Then, the rotational inertia is introduced into the Luenberger disturbance observer to observe the change of load torque, while estimating and compensating for the disturbance. The PI speed control method is replaced by a novel sliding speed control method. The proposed method can suppress the chattering caused by sliding variable structure and improve the response speed of the system while retaining the advantages of strong robustness of the SMC. Finally, the effectiveness of the method is verified by the simulation experiments and the semi-physical tests.