The omnidirectional all-wheel drive mobile robot supports single-wheel independent drive and steering, so it can adapt to complex and changeable terrain conditions by multiple sports modes. In the design of omnidirectional all-wheel drive mobile robot, engineers usually use flux-weakening control to improve the dynamic performance of Permanent Magnet Synchronous Motor (PMSM), so as to achieve better control results. However, there are many problems in the traditional flux-weakening control methods, such as difficult calculation and resource consumption, which makes it difficult to implement in MCU. According to the principle of PMSM, this paper will firstly analyze the characteristics of commonly used flux-weakening control methods. Secondly, on the basis of the traditional flux-weakening control method, this paper will propose an improved Maximum Torque-per-Ampere (MTP A) flux-weakening control method, and analyze the implementation process of the new model. Finally, this paper will verify the flux-weakening control method through simulation and experiments.