This work explores potential high-temperature superconductor materials in hydrogen-rich systems. Here, the crystal structure stabilities of ternary Ca–Sc–H systems under high-pressure (P = 100–250 GPa) and their superconductivities are investigated using the particle swarm optimization methodology combined with first-principles calculations. For the predicted candidate structures of Ca–Sc–H systems, the pressure-dependent phase diagram and thermodynamic convex hull were investigated across a wide range of compositions; the electronic properties of all the predicted phases were analyzed in detail to study the bonding behavior of these stable phases. We identified the crystal structures of four thermodynamically stable compounds: Rm-CaScH₆, Immm-CaSc₂H₉,C2/m-Ca₂ScH₁₀, and Rm-CaScH₁₂. Among them, Rm-CaScH₁₂ was predicted to have the highest T_c value (i.e., 173 K) at 200 GPa. The discovery of this previously unreported pressure-induced decomposition of Ca–Sc–H systems will pave the way for investigations on the nature of hydrogen–metal interactions.