In view of the problems such as fixed throttling area of throttle valve, long return pipeline high heating at valve ports, high energy consumption and explosive pipe used in the hydraulic excavator boom powered lowering system, measures such as increasing explosion-proof pipe valve, solenoid valve, pressure switch, controller and changing the function of multi-way valve were adopted, a hydraulic excavator boom unpowered lowering system with low heat, low energy consumption, stable start-up, simple structure, low cost and long service life was developed. The test results show that using the unpowered lowering system realizes energy saving and emission reduction, and the heat is reduced by nearly 50% compared with the powered lowering system, which reduces load for the heat dissipation system.