The low-speed gimbal system is a critical component of the control moment gyroscope (CMG), as its driving performance directly impacts the precision of the CMG’s output torque. Conventional test benches are characterized by complexity, high costs, and intricate testing procedures. Consequently, the electric motor emulator (EME) has emerged as a critical advancement in CMG testing techniques. This paper proposes a design scheme for an ultra-low speed permanent magnet synchronous motor (PMSM) emulator to meet the testing requirements of CMG gimbal electric drive systems under ultra-low speed conditions. Firstly, a parameterized PMSM model is developed to characterize the terminal properties of the motor. Subsequently, based on a three-phase two-level voltage source converter (VSC) topology, a power conversion control strategy for the EME is proposed. Finally, the design is validated through simulations and experiments. The results demonstrate that the designed EME accurately replicates the electrical and mechanical characteristics of a real motor, thereby meeting the ultra-low speed testing needs of CMG gimbal systems.