The invention discloses a piston pump comprising a piston, a pump cover, a pump body, a water inlet passage, a pressing chamber, a stop valve assembled between the pump cover and the pump body, a water outlet chamber formed between the stop valve and the pump body, and a water outlet passage formed in the pump cover. The stop valve separates the water inlet chamber and the water outlet chamber, and the water outside the piston pump may sequentially pass through the water inlet passage and the water inlet chamber into the pressing chamber. One end of the piston is movable in the pressing chamber to pressurize the water in the pressing chamber, and the pressurized water in the pressing chamber sequentially flows out from the pump cover through the water outlet chamber, the stop valve, and the water outlet passage. The piston pump is designed so that the water inlet chamber and the water outlet chamber are effectively separated by the stop valve. Thus, the positions of the water inlet chamber and the water outlet chamber are almost together, and the water inlet passage and the water outlet passage are integrated into the pump cover, so that the overall space utilization and layout aremore intensive and conducive to the miniaturization of the piston pump.