The atmospheric downward longwave radiation has great significance to surface energy balance and water cycle. Based on the observation data of radiation flux from September 2018 to August 2019 on the northern shore of the Qinghai Lake, the multi-temporal scale change characteristics of radiation flux were analyzed, and the applicability of ten parameterized formulas of atmospheric emissivity on sunny days was compared. And on this basis, the influences of clouds on atmospheric downward longwave radiation were quantitatively evaluated. The results show that each component of radiation had obvious and similar diurnal variation with ‘single peak’ pattern on the northern shore of the Qinghai Lake, and the radiations were higher during the day and lower at night. The radiative components except for upward shortwave radiation (mainly affected by land surface albedo) varied following air temperature during the year. Among ten parameterized formulas of atmospheric emissivity on sunny days, the applicability of Brutsaert formula was the highest on the northern shore of the Qinghai Lake. The atmospheric downward longwave radiation gradually enhanced with increase of cloud fraction (C_f). The cloud enhancement effect was less than 10 W·m^-2 when C_f was less than 10%, and exceeded 60 W·m^-2 when C_f was more than 75%. The ratio between the observation value of atmospheric downward longwave radiation on cloudy sky and corresponding calculated value on clear sky increased with increase of C_f, and there was a very significant quadratic function relationship between them. When C_f was less than 10%, the mean ratio was only 1.04, while when C_f exceeded 75%, the ratio was more than 1.25, so their quantitative relationship could better reveal the influence of clouds on atmospheric downward longwave radiation in this area.