As for the deep ultraviolet (UV) lithographic projection objective, the laser energy absorbed by the lens material causes temperature rise, which induces thermal aberration. Under the off-axis illumination mode, the temperature distribution is non-symmetric, and thus the research on the temperature distribution is significant for thermal aberration simulation, prediction and compensation.A temperature distribution function model is proposed to describe the three-dimensional temperature distribution of the lens in four illumination modes. Simultaneously, the relationship between temperature and exposure time is studied, and the temperature at the thermal steady state and the consumed time to get steady is calculated. The results show that the temperature distribution models perform well for describing the spatial temperature distribution of projection lens under several commonly used illumination modes with an average fitting error of about 10-3 ℃. The error of thermal steady temperature predicted via the relationship between temperature and time is about 10-4 ℃, and the time error is less than 3 min. The thermal aberration results calculated by the proposed model agree with the simulation results by SigFit, while the time cost shows a decrease of three orders of magnitude.