The heat exchange between watersurface and atmosphere determines the change of water temperature in the river,which is the main thermal factor affecting the ice condition and the formation of ice jams. We compared the performance of two existing nonlinear thermodynamic models and studied the influencing factors based on the analysis of net solar radiation, effective longwave radiation, evaporation and heat conduction characteristics in the freeze-up period of the Inner Mongolia reach of the Yellow River, China. Results show that the average hourly heat budget at the surface water-atmosphere interface during the freeze-up period was estimated to be 114.31 W/(m2·h) and 124.05 W/(m2·h) by Ashton’s and Shen & Chiang’s methods, respectively. Affected by the diurnal alternation of solar shortwave radiation and the large temperature difference between day and night in the Inner Mongolia, the daily average heat loss shows a regular changing pattern, which is the heat absorption in water surface is greater than heat release during the period of 11:00-15:00, but it is the opposite in the other periods.The contribution of meteorological factors of the total heat loss is as follows:temperature (Ta)>relative humidity (RH)>dew point temperature (Td)>wind speed (Va) and atmospheric pressure (P). The evaporation is more sensitive to the wind speed than heat conduction, but the effect of wind speed on the total heat loss is not significant. The dual effects of the sudden increase of wind speed and sudden drop of air temperature are the main factors speeding up the heat conduction, resulting in the occurrence of the extreme value of total heat loss. The total heat loss calculated by the two models are inconsistent when the wind speed is greater than 4 m/s, showing the differences between these two models and the corresponding influencing factors. To summarize, Ashton’s thermodynamic model is more applicable to the study of the ice density and condition during the freeze-up period of the Inner Mongolia reach of the Yellow River.