Abstract: The fluid loop is the most important part of the thermal control system on manned spacecraft.The fluid loop must meet the thermal requirement of all kinds of the conditions that may be occur during the whole period,working with other passive thermal control measure on spacecraft.At the same time,it should occupy the resource of the spacecraft as less as possible.The scheme and configuration of the fluid loop were determined basing on analysis and comparison.Considering the thermal design of target spacecraft to be docked with,the emphasis of the design was put on solving the thermal problems during the period of two spacecrafts combined together.The main requirements and emphases of designing fluid loop were presented.Based on the analysis of energy balance,two kinds of scheme were designed.And the performance of two schemes was compared.Finally,some suggestions on choosing working fluid of fluid loop system.