The construction of engineering projects cannot be separated from the support of a large number of geotechnical test data.In the conventional indoor geotechnical test methods,tri-axial shear test is a very important method to test the shear strength of rock and soil.Pressure source microcomputer servo system is a precision water pressure generator controlled by computer and driven by stepper motor.It is mainly used for precise control and measurement of confining pressure,back pressure and volume change in tri-axial tests.It can also be used as an independent constant pressure source to replace conventional indoor geotechnical test pressure sources such as weights,air compressors and seepage head,etc.The comparative test results show that the performance of the pressure source microcomputer servo system is stable,and the measurement accuracy of pressure and volume changes in tri-axial shear test is improved.It has the characteristics of high automation,high sensitivity and fast response.