A novel fast thermal aberration model for lithographic projection lenses is proposed. In the model, optical intensity calculation is simplified by using pupil intensity mapping, and simplified formulas for temperature calculation are derived to realize fast simulation of thermal aberration. The simulation results using the proposed model are compared with that of experiments carried out on a commercial lithography tool. The R-square of the simulation is better than 0.99 and the simulation time is about 10 minutes. Experiments and simulations show that the model is capable of predicting the thermal aberration or the variation trend of the thermal aberration of lithographic projection lenses fast and accurately. The model is applicable in projection lens design, evaluating degree of production risk posed by thermal aberration, etc.