The maximum frozen depth is the major index of the change in seasonally frozen soil. It is also an important parameter for the engineering design,construction and operation in seasonal frozen soil regions. The maximum frozen depth of seasonal frozen soil in Tibet from 1990 to 2014 were calculated by Stefan's method. The temporal and spatial variations of the maximum frozen depth were analyzed. The results indicated that the spatial distribution of the maximum frozen depth in Tibet had the characteristics of vertical zonality,latitude zonality and regional regularity,which had basically decreased from northwest to southeast from 1990 to 2014. In the context of global warming,the maximum frozen depth had decreased from 1990 to 2014. The maximum frozen depth had a negative correlation with the annual mean temperature and annual precipitation; the maximum frost depth decreased with the increase of annual mean temperature and annual precipitation. Beside,the response of maximum frozen depth to annual mean temperature was more significant than that to annual precipitation.