In order to implement the dual-objective optimization of load ratio of the combined ceiling radiant cooling panel and DOAS air-conditioning（CRCP-DOAS） system, BES-CFD co-simulation is introduced. Taking a residential room in Changsha with applications of CRCP-DOAS system as a research case, energy consumption of the system and indoor thermal environment are studied under different load ratio of three supply air temperature difference, and the optimal load ratio range is obtained from the perspective of energy saving, thermal comfort and safety. The results show that when considering the energy saving of the system, the optimal load ratio ranges are 46%~85%， 16%~85%, 3%~85% at the supply air temperature difference of 4 ℃，6 ℃，8 ℃，respectively. And it is more energy efficient when the supply air temperature difference is larger. From the perspective of thermal comfort, the optimal load ratio ranges are：20%~72%（4 ℃），16%~59%（6 ℃），3%~50%（8 ℃），respectively. And the load ratio has a larger adjustment interval when the supply air temperature difference is smaller. Under each load ratio, the surface temperature of ceiling and floor is higher than the air dew-point temperature near the surface, so there is no condensation risk. The optimal load ratio ranges are 46%~72%（4 ℃），16%~59%（6 ℃），3%~50%（8 ℃），respectively，under comprehensive consideration of energy efficiency，thermal comfort and safety.