For large-space steel structures in fire, an accurate temperature field model is essential to predict the temperature distribution for response analysis of the structure. Based on the field model theories of air thermodynamics and heat transfer, the combustion process and temperature distribution of large-space steel structures in fire were analyzed in this paper. The temperature field model of large-space fire, including fire source, smoke plume and smoke layers models, was established. Closed form formulas were developed to predict the air temperature, within its application limit, near the ceiling of large-space steel structures in fire. The accuracy of the formulas was verified by comparing with results obtained from numerical method based on field models. This research provides an important theoretical basis for further studying the behavior of large-space steel structures in fire.