The invention discloses a hydraulic process based on a water-injection pump hydraulic system. The process includes: a, a hydraulic reversing valve is on the left, a piston of a left hydraulic cylinder is at a certain position of the middle upper end, and a rod-end plunger of a right hydraulic cylinder is at a certain position of the middle; b, the piston continues moving down, and oil in a cavity is discharged through an internal hydraulically-controlled one-way valve; c, the one-way valve enters right-end space of a spool of the reversing valve and pushes the spool to move leftwards; d, main pump oil continuously pushes the piston to move down, meanwhile, the main pump oil enters upper cavities of the hydraulic cylinders and starts to push the piston to move down; e, the hydraulic cylinders start to discharge liquid at uniform speed and arrives the bottommost end; f, the oil pushes the piston of the left hydraulic cylinder to move down, then pushes the piston to move up, and pushes the oil in the upper cavities to flow back into an oil tank. The hydraulic process has the advantages of high pressure, high flow, simple structure, high efficiency, energy saving, long service life, displacement adjustability, ease of maintenance and operation, reversing accuracy and reliability, and capability of boosting.