In this paper

a digital identification method for a snowline is presented.The method takes into consideration that the lower limits of a perennially snow-covered area should only be deduced through contrasting with other limits.Thus

a method based on hydrological analysis was introduced to extract the snowline.Based on the digital elevation model（DEM） of the study area and the result of snow cover monitoring

the lowest point covered with snow could be recorded in one flow path. Through loop statements

all of the lowest points were determined by comparing the snow altitude in every flow path.The lowest points were then joined sequentially

according to the real landform

and shaped into snowlines.In addition

a method of computing the average annual snowline was analyzed.This method based on hydrological analysis can effectively avoid the influence of naked areas in snow cover

and shows promising results for the calculation of the lower boundary of a perennially snow-covered area.Spatial-temporal dynamics of snowlines can also be analyzed by the proposed method.The digital identification method presented here is effective at identifying a snowline

and could be helpful in rapid information extraction of a large-scale area.