The power density of a hydraulic pump is defined as the ratio of output power to its own weight.In fields such as deep-sea electromechanical,aerospace and bionic robots that have strict requirements on weight and volume,power density is an important indicator for the development and selection of hydraulic pumps.The power density characteristics of three types of hydraulic pumps (gear pumps,vane pumps and plunger pumps) of well-known hydraulic companies at home and abroad were compared based on the structure and material.The results show that:the power density of the hydraulic pump ranges from 0.18 kW/kg to 7.35 kW/kg,the maximum power density of the gear pump is 7.35 kW/kg,the vane pump is 5.41 kW/kg,and the swash plate piston pump is 3.54 kW/kg;the hydraulic pump with the force-balanced or automatic clearance compensation structure has a higher power density;the application of aluminum,titanium and other light alloy materials can significantly reduce the weight of hydraulic pump and improve the power density.This study provides reference for the design and selection of hydraulic pumps with high power density and lightweight.