Constant pressure control system and control method of variable pump

The invention discloses a constant-pressure control system of a variable pump. The constant-pressure control system comprises a feedback control valve group and a multi-way valve group, the feedback control valve group comprises a hydraulic control one-way valve; the multi-way valve group comprises a three-position six-way reversing valve; the state of the variable pump can be switched into the low-pressure standby mode and energy consumption is reduced by operating the reversing valve to be in the middle position, and the state of the variable pump can be switched into the constant-pressure control mode when the reversing valve is operated to be in the upper position or the lower position, so that the response speed is increased, namely, the load response time is saved; the three-position six-way reversing valve without load feedback is applied to the system to achieve constant-pressure control, the construction cost of the system is reduced, and low-pressure small-displacement standby and constant-pressure