Abstract: Any thermal event that has occurred during and after the formation of rocks can be traced in the rocks themselves. How to search these traces has been the focus of geological research in our country for a long time,and it is also a problem that needs to be solved as soon as possible. In recent years,results of studies by transimission electron microscopy (TEM),have shown that garnets occurring in different types of metamorphic rocks have undergone different degrees of plastic deformation.An intensive study on the extent and the characteristics of the deformation will be very useful in disclosing the history of metamorphism and deformation that the rocks have suffered. By determing the dislocation density of garnets one can roughly calculate the ancient differential stress tha the rocks have experienced to provide data for a model of tectonic evolution of the area concerned.