Abstract: Through the thermal coupling between ADS liquid lead bismuth target and lead based subcritical reactor, this paper studies the effect of whether a thermal barrier layer is added between the target and the reactor, the thermal conductivity and thickness of the layer, and when a gas thermal barrier layer is added, gas pressure on the heat flow between target and reactor. The study found that adding a thermal barrier layer can reduce the heat flow after coupling. Adding a gas layer can significantly reduce the heat flow, and allow the flow velocity of lead-bismuth in both target and reactor and the temperature difference between target and reactor to fluctuate over a wider range. The heat flow is proportional to the thermal conductivity of the thermal barrier layer and inversely proportional to the thickness of the layer. The thickness of the gas layer can be selected between 0.06 m and 0.08 m. The pressure of the gas thermal barrier is in the range of 0.1 to 10 Pa, and the heat flow varies significantly with the pressure. Therefore, the pressure of the gas thermal barrier layer can be selected to be about 0.1 Pa.