The invention relates to a precision pressure control system and a hydraulic machining method of a servo pump control hydraulic machine. The hydraulic machine comprises a medium-flow servo pump and alarge-flow servo pump driven by a servo motor, outlet pipelines of two pumps are connected with a main cylinder upper cavity oil way through a seventh dynamic valve, and the main cylinder upper cavityoil way is further connected with an oil tank through a fourth dynamic valve and a proportional valve; a main cylinder lower cavity pipeline is connected with an outlet of a ninth cartridge valve, aninlet of the ninth cartridge valve is connected with the oil tank through a fifth cartridge valve and an eighth cartridge valve, the fifth cartridge valve supplies supporting force during deceleration and pressurization through an overflow valve, and the eighth cartridge valve is turned on during the return stroke. In hydraulic machining, each working cycle comprises the following actions of automatic pressure compensation for an energy accumulator, pressure supplementation stopping for the energy accumulator, rapid descending of a sliding block, deceleration pressurizing of the sliding block, pressure maintaining of the sliding block, pressure relief of the sliding block, and return and stopping of the sliding block. The servo driver is switched in two modes of flow control and PID regulation control, stable pressurization of the sliding block is achieved, the phenomenon that a part deforms due to pressurization overshoot is avoided, and pressure relief is stable.