Abstract: In order to verify the design rationality and manufacturing reliability, it is necessary to carry out the steady-state irradiation test for a new fuel assembly in the high temperature and high pressure water test loop. Thermal optimization strategies to satisfy the requirements of fuel assembly radiation test parameters for the heat exchange system as the regenerative heat exchanger in the steady-state irradiation test loop were studied, including regeneration section structure improvement, heat exchange area margin selection and multiple heat exchanger connection mode. It shows that there is no significant effect on improvement of the heat exchange capacity under low parameters with the constant regeneration section structure and heat exchange area, no matter what flow rate and temperature of the primary water are used. It has an obvious effect on increasing the heat exchange power of the heat exchanger at low parameters that short-circuited water bypass pipes in the regeneration section are set. The heat exchange area with a reduction of 30% in the regeneration section can effectively increase the heat exchange power by 25.6%. With the remaining heat exchange area margin under the initial design conditions, compared to that in the design condition, the decrease in the primary water operating temperature will enhance the compensation effect of the heat exchange area margin on the heat exchange power, and a decrease in the primary water operating flow will weaken this compensation effect. The heat exchange system in the steady-state test loop should be designed as a series-parallel switchable scheme to satisfy the wide range of power requirements. When the total flow of the primary water with inlet temperatures of 250 ℃ and 330 ℃ is 40%, the maximum heat exchange power of the two heat exchangers in series compared with the single operation will increase by 81% and 77%, respectively.