Recently, a united symmetry-protected topological crystalline insulator (TCI) $\mathrm{NaC}{\mathrm{d}}_4\mathrm{A}{\mathrm{s}}_3$ has been discovered experimentally, which further features a temperature-driven transformation from TCI to TI due to the mirror symmetry broken across a rhombohedral-to-monoclinic structural transition. Here, we report the pressure tuning of structural property and emergence of superconductivity in TCI $\mathrm{NaC}{\mathrm{d}}_4\mathrm{A}{\mathrm{s}}_3$ by comprehensive high-pressure experiments in diamond-anvil cell. Temperature-dependent Raman measurements show that the structural transition temperature gradually reduces upon compression and is completely suppressed above $\sim 4$ GPa. The stable rhombohedral phase further undergoes amorphization evidenced by synchrotron x-ray-diffraction result, which sets in at 20.7 GPa and completes at 34.4 GPa. Along with the complete amorphization, the metallization and superconductivity with a critical temperature $T_c\sim 2.5$ K appear simultaneously, as observed in transport experiments. We argue that the sudden enhancement in $T_c$ across 60.0 GPa is likely related to the pressure-driven amorphous polymorphism. Our finding unravels the fundamental structure-property relationship and highly tunable crystallographic symmetry in $\mathrm{NaC}{\mathrm{d}}_4\mathrm{A}{\mathrm{s}}_3$ by external pressure, potentially sparking further investigations via alternative tuning strategies.

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• Phase transitions
• Pressure effects
• Superconductivity
• Crystalline systems
• Topological materials
• Pressure techniques