The invention discloses a structure-improved liquid phase plunger pump. The structure-improved liquid phase plunger pump comprises a high-pressure cavity and a low-pressure cavity, wherein an inner cavity opening is formed in the rear side of the low-pressure cavity. The structure-improved liquid phase plunger pump further comprises a plunger rod and a dustproof cover, wherein a pressing plate is fixed to an opening in the rear side of the dustproof cover, a spring is arranged in the dustproof cover, the dustproof cover is assembled on the plunger rod as a whole and installed on the cavity opening in the rear side of the lower-pressure cavity, the front end of the plunger rod penetrates into an inner cavity of the high-pressure cavity and an inner cavity of the low-pressure cavity, the rear end of the plunger rod stretches out of the pressing plate and is fixedly connected with one ejector rod, and annular table is arranged on the rod body of the plunger rod and is sleeved with a supporting ring, the front end face of the supporting ring is pressed on the spring in an abutting mode, and the pressing plate is tightly pressed on the rear ring face of the supporting ring. According to the structure-improved liquid phase plunger pump, dust and impurities can be prevented from falling onto the working surface of the plunger rod, abnormal abrasion between the plunger rod and a high-pressure sealing ring in the high-pressure cavity as well as a low-pressure sealing ring in the low-pressure cavity is reduced, meanwhile, high coaxiality between the plunger rod and the ejector rod is not needed, and therefore machining difficulty and cost can be reduced.