Precisely constraining the shock pressure of a Mars sample is critical for revealing the shock condition, geological process, and habitability of the Martian surface. The crystal structure of plagioclase is sensitive to the moderate shock pressure, such that its infrared spectra may record the shock state of Martian materials. In this study, we present a new way for quantifying the shock pressure via the micro-FTIR spectra of plagioclase by re-analyzing the published spectra of experimental shocked feldspars. Using the absorption area of micro-FTIR in the range of ∼1,000–1,150 cm⁻¹, the shock pressures of plagioclases from three types of Mars meteorites were constrained. The results show that the nakhlite Northwest Africa (NWA) 10645, shergottite Tindouf 002, and martian breccia NWA 11220 have the shock pressure of 18.5 ± 5.2 GPa, >30 GPa, and 0–24.2 GPa, respectively. Our work demonstrates that the micro-FTIR spectra of plagioclase is not only a quantitative tool for constraining the moderate shock pressure (<30 GPa) of Martian materials but also a useful technique for recognizing the high-pressure phase maskelynite from plagioclase-glass and evaluating the shock effects of Mars samples. In the future, this method will be available for the analysis of Mars samples returned by China's Tianwen-3 mission in around 2030.