Thermal deformation of 16 nm extreme ultraviolet lithography (EUVL) objective is one of the main factors influencing its high resolution imaging. In order to provide a reliable technical basis for the thermal management of EUVL system, we simulate the thermal deformation of a typical 16 nm EUVL objective with 0.33 numerical aperture. The finite element software ANSYS is used to simulate the transient temperature and thermal deformation of each mirror during exposure. The deformed mirror surface is fitted with Zernike polynomial as an interface tool to evaluate the effect of the thermal deformation on imaging performance. The results show that the maximum temperature rise and the maximum thermal deformation of the objective are 3.9 ℃ and 10.2 nm, respectively. The thermal deformation of the objective in the high temperature state causes maximum wavefront error root mean square (RMS) of 0.1λ and the distortion of 56 nm, which are beyond the reasonable range. The wavefront error RMS and the distortion caused by the thermal deformation of M3 and M4 mirrors together account for 88% and 99%, which play leading roles in the imaging performance. The temperatures of these two mirrors should be controlled strictly.