Aimed at the application of pump motor in the pressurization system of diamond cubic press, the design of motor protector device is completed based on STM32 microprocessor with the characteristics of common faults and reasons being analyzed. The hardware circuits were designed, the fullwave integral sampling algorithm was adopted, and the establishment of fault identification strategy was established especially aimed for motor starting frequently, so as to achieve following functions of the device, such as block up protection, overload protection, lacked phase protection, phase imbalanced protection and so on. Manual reset was needed under the faulty condition. The motor working information was sent to the press control system through the I/O modules and RS485 communication modules. It can provide qualifications to the diamond synthesis monitoring control and troubleshooting.