Abstract: Through the improvement of type SVF-1E-01 Electric-hydraulic Servo Fatigue Testing Machine, the application of virtual instrument technology in apparatus improvement was studied. Based on PCL-812pg DAS Card, Virtual Oscilloscope Program and Virtual Signal Generator Program were designed with Delphi 5.0 and OOP technology on Windows 98 operating system. The improvement of the fatigue testing machine was accomplished, which enlarged the experimental range and improved the precision. The whole system includes the following links: the sampling and dynamic displaying of analog signal; the generation and output of simple or composite signals. The developed software system was convenient to use with the characteristics of visual and direct viewing. The results revealed that the precision of controlling signals was high enough to meet the demands for testing.