The invention discloses a vehicle-mounted air purifier and an air quality prompting method thereof, relates to air purifiers and aims at providing the vehicle-mounted air purifier. The vehicle-mounted air purifier has the advantage that users conveniently detach a shell to remove impurities in the shell. The key point of the technical scheme of the vehicle-mounted air purifier is that the shell comprises an upper shell and a lower shell; an air inlet and an air outlet are formed in the upper shell; a filtering component and a fan are arranged in the lower shell; a plurality of clamping blocks I are arranged in the circumferential direction of the outer wall of the upper shell; clamping blocks II corresponding to the clamping blocks I are arranged in the circumferential direction of the inner wall of the lower shell; the sizes of the clearances between the adjacent clamping blocks II are smaller than the sizes of the clamping blocks I; clamping grooves for the clamping blocks I to slide in are formed in the clamping blocks II; the outer wall of the upper shell is connected with a locking sleeve in a threaded manner; and one end, close to the lower shell, of the locking sleeve is connected with the outer wall of the lower shell in a threaded manner.