In order to reduce the influence of load torque disturbance on the low speed stability of hybrid excitation synchronous motor and improve its load-bearing ability at low speed, a low speed control strategy of Hybrid Excitation Synchronous Motor based on a load torque sliding mode observation is proposed. The load torque observed by sliding mode observer are taken as the feedforward compensation of q-axis current and the given input of excitation current respectively. Furthermore, the load-bearing ability and stability of the hybrid excitation synchronous motor are improved. The sliding mode surface is composed of the difference between the actual speed and the estimated speed, which is used to realize the load torque observation in the sliding mode observer. The simulation results show that the value of the load torque observed by the observer is accurate, and the dynamic characteristics and robustness of the hybrid excitation synchronous motor in low speed range can be improved by the low speed control strategy.