Abstract: A simple methord of determing emissivity of surface using Eppley pyrgeo-meter in situ in order to evaluate surface temperature is presented. The indicated temperature of radiometer need corrections for actual sky thermal radiance and for true surface emissivities. Based on comparisons between radiation temperature and surface mercury-thermometer temperature at Nagqu, northern Tibetan during December 1985-January 1986, it was observed that their differences were mostly within 2-4℃.