The utility model discloses a subassembly is fixed to car vacuum pump impeller, include the casing and set up the lower washer on the casing, and set up the cam circle on lower washer, reach the upper cover that the setting circled at the cam, and locate the impeller subassembly in the cam circle, all be provided with heavy groove on the upper and lower both ends face of cam circle, lower washer arranges heavy inslot in with the upper cover, and lower washer, upper cover and cam circle are fixed through multiunit screw rod and casing, the fixed subassembly of this impeller circles at the cam and has set up heavy groove, upper cover and lower washer all set with heavy inslot, can effectively improve sealed effect, the assembly operation of also being convenient for more simultaneously is that the screw of each part corresponds the assembly operation of being convenient for more.