The crash box is a structure designed to absorb energy during a collision and is widely used in the automotive field. In this paper, the energy absorption capacity and impact resistance of different geometric forms of the crash box, along with the variation in the thickness of the thin walls of the crash box, are compared during axial compression from the same type of ST37 mild steel and conducting finite element analysis in the Ls-Dyna software. From the theories and finite element analysis results, the force and displacement curves of the specimens for each case provide detailed results on the changes in force during the deformation process. The energy absorption capacity (E), specific energy absorption value (SEA), and crushing force efficiency (CFE) were calculated, evaluated and compared among the crash box with square, circular, hexagon, and dodecagon cross-sections with a thickness of 1.5 mm. The results show the hexagonal impact box has the highest energy absorption capacity and crushing force efficiency. Then, these parameters were evaluated and compared with the models with larger wall thickness, which showed better specific energy absorption value and crushing efficiency. These findings are expected to open new research directions on energy absorption mechanisms during collisions.