Sliding friction experiments of wet multi-disc clutch with different frictional pairs under braking condition in the SAE#2 test bench are designed to investigate the friction torque attenuation phenomenon. The attenuation coefficient of friction torque of wet multi-disc clutch is proposed to describe the decrease degree of the tested friction torque. According to the test data of friction torque transferred by two and six frictional pairs respectively, the calculation formula of attenuation coefficient for two-six frictional pairs is fitted and the influences of relative rotational speed and average pressure on attenuation coefficient are analyzed. The results show that the attenuation coefficient is influenced by attenuation value of friction torque and calculated friction torque. Under the full oil film condition, the attenuation value of friction torque decreases with the rise of the relative rotational speed and increases while the average surface pressure increases. In general, the attenuation coefficient declines with the rise of the relative rotational speed, and when the average surface pressure increases, the coefficient increases first and then decreases.