Abstract: Direct drive hydraulic servo system is a kind of global energy-saving power system considering power matching from the power source,which is widely used in many fields. The working principle and structural composition are analyzed in the paper,and the principle and effect of energy-saving are discussed. The speed regulation range and influencing factors of the technology are analyzed,and the estimation method of speed regulation range is proposed. The result of test and application verifies the correctness and rationality of the analysis and the applicability of the technology on the testing machine.