The prediction of thermal effects in lithography projection objective plays a significant role in thereal-time dynamic compensation of thermal aberrations. For the illuminated lithography projection objective,this paper applies finite element analysis to get the temperature distribution, surface deformation and stressdata. To improve the efficiency, a temperature distribution function model is proposed to use for thesimulation of thermal aberrations with the help of optical analysis software CODE V. SigFit is approvedintegrated optomechanical analysis software with the feature of calculating OPD effects due to temperaturechange, and it is utilized to prove the validation of the temperature distribution function. Results showthat the impact of surface deformation and stress is negligible compared with the refractive index change;astigmatisms and 4-foil aberrations dominate in the thermal aberration, about 1.7 λ and 0.45 λ. The systemtakes about one hour to reach thermal equilibrium and the contrast of the imaging of dense lines get worseas time goes on.