Abstract: This paper firstly suggests a method of calculating the volume change of the firn based on the DEM data sets which are for the same area,acquired at the same season,but in different years,and during this period no obvious geological disasters occurred in the studying area.Secondly,two methods for calculating the volume change of the firn are introduced: one is based on the regular square grids(RSG),another uses the triangulated irregular network(TIN).The verification experiments calculated from the same original DEM data acquired in 1962 and 1990 respectively for the drainage area of Urumchi River Basin in Tianshan Mountain are introduced and have proved that it is feasible and accurate to calculate the firn's volume change in the study area using DEMs of different time phases where no obvious geological disasters have occurred.