A complete hydraulic power unit consists of five parts, namely the working medium, power part, execution part, control part, and auxiliary part. The working medium is used to transmit motion and power in the hydraulic power unit, and the commonly used working medium is hydraulic oil. The core component of the power part is the hydraulic pump, which converts the mechanical energy output by the prime mover into liquid pressure energy and inputs it into the hydraulic power unit. The core element of the executive part is the hydraulic cylinder or hydraulic motor, which converts the pressure energy of the liquid into mechanical energy to drive the working mechanism.

The control part is mainly composed of three types of control elements, which are used to control or adjust the pressure, flow, or direction of the oil in the hydraulic power unit to ensure that the execution device completes the expected work. In the currently commonly used hydraulic transmission system, various movements of the hydraulic power unit are mainly realized by the hydraulic control element controlling the hydraulic actuator to change the direction of movement, the carrying capacity, and the speed of the movement.

The control elements mainly include directional control elements, pressure control elements, and flow control elements. Auxiliary components connect the previous parts together to form a system, which mainly plays the roles of oil storage filtration, measurement, and sealing in the hydraulic power unit.