Abstract: In the thermal control system of a spacecraft, the performance of the pump-driven fluid loop system is of paramount importance. This study investigates the gas transport hysteresis phenomenon within the slit structure of the accumulator, analyzing the dynamic behavior of gas molecules in the slit through experimental methods and numerical simulations using COMSOL Multiphysics. The results indicate that the average residence time of gas molecules is the primary factor contributing to transport hysteresis. This finding is of significant importance for understanding and predicting the gas transport characteristics in the pump-driven fluid loop system under vacuum conditions. The study provides a scientific basis for optimizing the design of the pump-driven fluid loop system, thereby enhancing the efficiency and reliability of spacecraft thermal control systems.