In order to overcome the disadvantages of traditional expanding machine,such as high energy consumption,low efficiency,etc,according to its working features,improvement to the system was made.Combining with the development trend of modern hydraulic technology,the direct drive volume control technology was applied to the hydraulic system of expanding machine.By analyzing the new system,the result shows that the improved hydraulic system has the advantages of energysaving,high efficiency,simple structure and high control precision.The improved method is feasible and has wide application prospect.