Thin-walled tubes are classic energy-absorbing structures, and corresponding crashworthiness topology optimization methods have been extensively developed [1-2]. Among these, the equivalent static load method (ESLM) and the hybrid cellular automata (HCA) have been integrated into commercial software. Fundamentally, the objective of crashworthiness topology optimization for energy-absorbing structures is to determine the optimal configuration under finite mass and specific boundary conditions [3]. However, direct optimization processes often necessitate specific mass constraints. Furthermore, due to the lack of explicit identification of plastic hinges, the resulting unstable energy-absorption process may fail to satisfy the requirements for progressive deformation. To achieve progressive energy absorption, this paper proposes a nested topology optimization methodology for the crashworthiness of thin-walled tubes based on relative element density. In the outer loop, the thin-walled tube is segmented based on the theoretical folding element height, followed by non-linear dynamic simulations. Under given crushing force boundary condition, the mass constraints for different energy-absorbing segments are calibrated to determine the feasible range of multi-stage stiffness within the tube. In the inner loop, manufacturing and mass constraints are introduced, and the topology optimization of different segments is performed using the ESLM. The nested loops iterate until the convergence criteria are met. Numerical examples and optimization results are presented to demonstrate the feasibility of the proposed methodology, with a specific focus on the convergence rate of the crashworthiness optimization for energy-absorbing structures.