A handheld high-pressure cleaning machine powered by using a direct current and connectable to an external water source by using a water pipe, wherein the handheld high-pressure cleaning machine comprises an integrated spray gun comprising: a motor, a transmission mechanism connected to the motor and a pump driven by the transmission mechanism sequentially arranged from the rear to the front of the spray gun in a housing; a nozzle connected to a water outlet of the pump at the front of the spray gun whereby water from the external water source may be sprayed out through the nozzle; a handle for gripping having a front end and a rear end formed on or connected to the housing with the front end of the handle behind the motor; and a detachable rechargeable battery pack external to the handle and located at the rear end of the handle; wherein the pump comprises a water inlet chamber, a water outlet chamber and a central chamber connected to the water inlet chamber and the water outlet chamber, wherein a plunger is disposed in the central chamber and an eccentric mechanism comprising an eccentric shaft and a rotating shaft is connected to the plunger, and the eccentric mechanism drives the plunger to perform reciprocating motion in the central chamber; wherein the center of the plunger is provided with a mounting portion connected to the eccentric shaft, a mounting bearing is disposed between the mounting portion and the eccentric shaft and a support bearing supports the rotating shaft in the housing; and wherein the handle is obliquely arranged, so that the center of gravity of the high-pressure cleaning machine is located within a range from 8 centimeters behind a rear endpoint of the handle to 8 centimeters in front of a front endpoint of the handle. a motor, a transmission mechanism connected to the motor and a pump driven by the transmission mechanism sequentially arranged from the rear to the front of the spray gun in a housing; a nozzle connected to a water outlet of the pump at the front of the spray gun whereby water from the external water source may be sprayed out through the nozzle; a handle for gripping having a front end and a rear end formed on or connected to the housing with the front end of the handle behind the motor; and a detachable rechargeable battery pack external to the handle and located at the rear end of the handle; wherein the pump comprises a water inlet chamber, a water outlet chamber and a central chamber connected to the water inlet chamber and the water outlet chamber, wherein a plunger is disposed in the central chamber and an eccentric mechanism comprising an eccentric shaft and a rotating shaft is connected to the plunger, and the eccentric mechanism drives the plunger to perform reciprocating motion in the central chamber; wherein the center of the plunger is provided with a mounting portion connected to the eccentric shaft, a mounting bearing is disposed between the mounting portion and the eccentric shaft and a support bearing supports the rotating shaft in the housing; and wherein the handle is obliquely arranged, so that the center of gravity of the high-pressure cleaning machine is located within a range from 8 centimeters behind a rear endpoint of the handle to 8 centimeters in front of a front endpoint of the handle.