The invention discloses a power split type hydraulic hybrid power system of a loading machine. The power split type hydraulic hybrid power system of the loading machine is composed of an engine, a first hydraulic pump/motor, a second hydraulic pump/motor,, a hydraulic work system, a planet row, a transmission gear, a first transmission shaft, a second transmission shaft, a third transmission shaft, a first locking device, a second locking device, a high pressure accumulator, a low pressure accumulator and a hydraulic control check valve. The power split type hydraulic hybrid power system of the loading machine uses a planetary gear train compact in structure as a power coupling element to achieve power split type transmission for the loading machine. A composite planetary gear train is used as a transmission system of the power split type hydraulic hybrid power system of the loading machine, and only comprises two locking deices, and thereby easily achieves automatic control, and is high in integration degree. The power split type hydraulic hybrid power system of the loading machine abandons a hydraulic torque converter, improves efficiency of the transmission system, and reduces oil consumption of the loading machine. The power split type hydraulic hybrid power system of the loading machine can achieve hydraulic continuous speed change, enables the engine to work in a high efficiency area, and reduces the oil consumption.