The invention discloses a torque loading system of a hydraulic pump. The system provides a control oil source additionally for a proportion overflowing valve at an outlet of the hydraulic pump; as being passed by oil all the time, the proportion overflowing valve can be in better working characteristics, and can carry out torque loading for the hydraulic pump with low rotating speed, even zero rotating speed. Simultaneously, the torque loading system uses the electronic elements of a potentiometer, an electronic switch, a button and the like to form a torque loading control module, adjusts theloaded torque by adjusting external control signals or the potentiometer, and realizes impact loading and impact unloading of the torque by the button, thus leading the loading system to have the functions of impact loading, impact unloading and continuous loading and the like. Besides, the pressure valve of the provided control oil is equal to the highest working pressure of the proportion overflowing valve so as to guarantee that the control oil can enter the proportion overflowing valve by a one-way valve under any condition and increase the range of loading the torque of the torque loading system.