Abstract: To evaluate the peak load and early post-peak load-retention capacity of carbon fiber reinforced polymer (CFRP) thin-walled cylindrical shells under axial compression, two comparative numerical conditions were established, namely an undamaged geometrically nonlinear post-buckling path and a damage-coupled post-buckling path. A standard post-peak window was defined from the peak point to the first 10% load reduction point. Within this window, a load-path difference \eta _\rmP(s) and a damage-related energy ratio \zeta (s) were introduced, and the activated failure region was further used to characterize the spatial distribution of stiffness degradation after intralaminar failure. The results show that the balanced shear-participating layup S2 reaches a peak load of 67.63 kN, higher than 60.26 kN of the balanced orthogonal layup O2, whereas its standard post-peak window is only 0.00390 mm, approximately 16.5% of that of O2. In the O-series, O2 gives a higher peak load while O1 provides a longer post-peak window; in the S-series, S1 and S2 show high-peak short-window responses, while S3 shows a low-peak long-window response. The combined use of \eta _\rmP(s) and \zeta (s) identifies several post-peak degradation modes, including damage-energy concentration within a short window, progressive path modification, and path-sensitive response with a low energy ratio. The proposed windowed path-energy evaluation method provides quantitative indicators for layup comparison and failure-mechanism interpretation of CFRP thin-walled cylindrical shells.