Abstract: By using MTS series 815.02 model servo-controlled stiffrock mechanics testing system, the stress-strain characteristicsof the sandstone specimen were studied in unloading process under tri-axialcondition with different unloading rates. The relation between strength and unloadingrate was analyzed and a formula was obtained.The fracture mechanism in unloading process was studied by observing thecrack characteristics. The findings can provide sometheoretical reference for engineering practice when analyzing the rock massunloading problems.