Variable-frequency water pump capable of improving electromechanical coupling of water machine

The variable frequency water pump comprises a volute (1), a centrifugal impeller (2), a rotating shaft (3) and a variable frequency motor, the centrifugal impeller is installed on the rotating shaft and installed in the volute, and the rotating shaft is connected with the variable frequency motor through a coupler; the centrifugal impeller comprises a first part and a second part which are separately arranged, the first part comprises a rear disc (21), first half blades (22) and a hub (23), the multiple first half blades are distributed in the circumferential direction of the rear disc, the second part comprises a front disc (24) and second half blades (25), the multiple second half blades are distributed in the circumferential direction of the front disc, and the hub (23) is arranged in the front disc. The first half blade and the second half blade are matched with each other to form a complete impeller blade, and the first part can axially move relative to the second part, namely, the axial position can be