In order to explore a lightweight and high-efficiency thermal insulation technology in aerospace cryogenic field, and investigate variable density multi-layer insulation structures which meet requirements of weight and insulation performance, two types of variable density multi-layer insulation structures were summarized. The Layer-by-layer heat transfer model was used to simulate heat flux and inter-layer temperature distribution characteristics of two types of variable density multi-layer insulation structures, and the characteristics were compared with the uniform density multi-layer insulation structure. The results show that when the weight remains the same, the heat flux is significantly lower than that of the uniform density multi-layer insulation structure by reducing the relative density of spacers in the low-density zone and increasing the thickness of the spacer, which is a lightweight and excellent cryogenic thermal insulation technology suitable for cryogenic liquid storage. The research clarifies the variable density multi-layer insulation structures that offer advantages in weight and insulation performance, and provides a reference for future research on the optimization of variable density multi-layer insulation structures.