Equivalent experimental conditions to those in space were used to characterize the effective thermal conductivity of the fiber fabric insulation used in the multilayer insulation system of the material preparation furnace loaded on Tiangong-2 Space Station. By evaluating the material following variations in the on-orbit temperature and on-track pressure, the microscopic heat transfer mechanism was studied. The furnace internal temperature field under different working conditions was also simulated according to the characterization results, and the data reliability was verified. The results showed that the effective thermal conductivity of the fiber fabric increases non-linearly with rising temperature; moreover, with lower pressures, the growth trends are gentler. With a pressure drop, the results present the trend of a decaying exponential function with a critical pressure value. Radiation and gas phase heat conduction are the main factors affecting the heat transfer of the fiber fabric under the microgravity environment. Simulation results of the temperature field demonstrate that the temperature field distribution trend matches well with that of the measured results. The maximum calculation error of the furnace center is 1.3% of the measured temperature. This method can be used to evaluate the thermal insulation performance of the multilayer fiber material close to the practical working conditions more reasonably, and also to improve the accuracy of thermal simulation prediction models.