Abstract: The VCS composite insulation structure can effectively reduce the evaporation loss.At present,there is still no comprehensive optimization design for the VCS composite insulation structure.The existing research methods cannot accurately reflect the accurate relationship among the heat flux and the thermal conductivity of the Variable-Density Multilayer Insulation (VD-MLI) and the cold screen position.This paper considers the thermal conductivity of VD-MLI with the change of cold screen position,studies the interaction law of VCS position and VD-MLI,and analyzes the best density of VD-MLI and the best position of VCS.The research results indicate that after adding the air-cooled screen,reducing the density of the medium-density layer and increasing the density of the high-density layer can further reduce the heat leakage.For different combinations of layer densities,there is an optimum screen temperature that minimizes heat leakage when the cold screen is at this temperature.