The invention discloses a three-cavity sliding-vane-type vacuum pump. The vacuum pump comprises an air suction end cover (1), a pump cavity (2), sliding vanes (3), a rotor (4) and an exhaust end cover(5). A three-working-cavity structure is adopted, three identical closed working cavities are formed among the air suction end cover (1), the pump cavity (2), the exhaust end cover (5) and the rotor(4), the formed closed working cavities are asymmetric working cavities, and the volume of the part, near a corresponding exhaust port, of each working cavity is smaller than the volume of the part, near a corresponding air suction port, of each working cavity. In the working process, the relative positions of the sliding vanes in the different working cavities at any moment are different, therefore, the working steps of the working cavities are not consistent, the three working cavities can be prevented from exhausting air at the same time, and the pulsation of the exhaust gas flow can be reduced. According to the vacuum pump, the inner volume ratio of the three-cavity sliding-vane-type vacuum pump is remarkably improved, the limit vacuum degree of the three-cavity sliding-vane-type vacuum pump is effectively improved, and the problems of vibration and noise caused by exhaust flow pulsation are solved.