Abstract: A plurality of the flow path in the Thermal Insulation Structure（TIS） is connected by a discrete tube distributed in a circumferential direction. The analysis of accurate flow and heat transfer of the entire device requires a three-dimensional fine calculation model which is time-consuming for model meshing and computation. In order to meet the needs of the design and structural optimization of the initial stage of the design, a temperature field approximation method is proposed for TIS containing the circumferential discrete pipelines, based on the equivalent area of through-flow and the equivalent circumferential speed. Numeral calculations are used to analyze the internal flow field of TIS. The results of flow field, temperature field and pressure field between the three-dimensional real model and the approximate model are compared. The result of the approximate analysis model is the same as that of the three-dimensional real model. It is suitable to use the approximate analysis model to obtain the result of fluid flow and heat transfer at the early stage of TIS design.