The control of the hydraulic pump is realized by adjusting its variable swing angle. According to the different control forms, it can be divided into three categories: power control system, flow control system and combined control system. The power control systems include constant power control, total power control, pressure cut-off control and variable power control; flow control systems include manual flow control, positive flow control, negative flow control, maximum flow two-stage control, load sensing control and electrical Flow control, etc.; the combined control system is the combined control of power control and flow control, and is most widely used in hydraulic control machines.