Abstract: To investigate the auxiliary heat flux for temperature control in the thermo-mechanical package of cryogenic targets, a 2-D axial symmetric computational fluid dynamics model for thermo-mechanical package with a radiation shield and storm window was established. By considering the effects of radiation heat transfer outside the thermo-mechanical package and the gas pressure filled-in the thermo-mechanical package, the temperature field of the cryogenic target was solved with FLUENT software. The results show that rational selection of the heat fluxes in both the upper and lower auxiliary heating zones and their differences enables the maximum temperature difference of the target surface to be less than 0.1 mK. As the radiation intensity and the gas pressure increase, the maximum temperature difference of the target outer-surface increases, as well as the optimized difference of the upper and lower auxiliary heat fluxes increases to fulfil the requirement of temperature uniformity on the target outer surface.