This study explores the crashworthiness performance of square structures inspired by the cross-sectional geometry of a seahorse skeleton, made from polyethylene terephthalate glycol reinforced with carbon fiber (PETG-CF). Three key parameters were studied, including inner shape, inner diameter, and rib thickness, each varied across four levels. Quasi-static axial compression tests were conducted to assess the crashing performance of the specimens. Detailed failure histories were documented, and data on crash load, absorbed energy, and displacement responses were recorded. To evaluate crashworthiness, several indicators were analyzed, containing the initial peak force ( F ip ), the energy absorption (U), the mean force ( F m ), the specific energy absorption (SEA), and the crash force efficiency (CFE). Analysis of variance (ANOVA) was employed to quantify the percentage contribution of each studied parameter to the crashworthiness indicators. An integrated multi-attribute decision-making (MADM) approach, merging the analytic hierarchy process (AHP) and the technique for order of preference by similarity to ideal solution (TOPSIS), was utilized to identify the optimal structure for improved crashworthiness performance. The ANOVA results reveal that inner shape predominantly influences F m (53.31%) and U (53.45%), inner diameter has the greatest effect on SEA (38.33%), and rib thickness contributes most significantly to F ip (50.46%) and CFE (63.51%). Furthermore, the AHP-TOPSIS results indicated that the P30/T5 configuration exhibited the best overall crashworthiness performance, achieving F ip = 22.20 kN, U = 1105.22 J, F m = 19.74 kN, SEA = 19.08 J/g, and CFE = 0.889. This superior performance is attributed to the well-balanced combination of the crashworthiness indicators.