$M_3{A}_{2}X$ phase is a type of ternary layered MAX-phase-like materials. To date, only four stable $M_3{A}_{2}X$ phases have been discovered. In this research, high-throughput density functional theory calculations were employed to systematically identify stable $M_3{A}_{2}X$ phases and then predict their properties. Starting from 240 possible compositions and 51 structural models for each composition, 12 $M_3{A}_{2}X$ phases successfully passed three rounds of stability assessment (thermodynamic, dynamic, and mechanical stabilities) and thus are stable. Crystal structures of stable ${\mathrm{Sc}}_3{\mathrm{S}}_2\mathrm{C}, {\mathrm{Y}}_3{\mathrm{S}}_2\mathrm{C}$ and ${\mathrm{Y}}_3{\mathrm{Se}}_2\mathrm{C}$ are novel and different from those of synthesized $M_3{A}_{2}X$ phases. The electrical conductivities of the 12 $M_3{A}_{2}X$ phases are generally superior to those of corresponding classic $M_{2}AX$ phases, while their mechanical properties are slightly inferior. Through the comparison of bond strengths using the crystal orbital Hamilton population analysis, it has been discovered that $M_3{A}_{2}X$ phases have a greater tendency to exfoliate into 2D MXenes than $M_{2}AX$ phases. Among them, the ${\mathrm{Zr}}_3{\mathrm{Se}}_2\mathrm{C}, {\mathrm{Zr}}_3{\mathrm{S}}_2\mathrm{C}$, and ${\mathrm{Sc}}_3{\mathrm{S}}_2\mathrm{C}$ phases exhibit the highest exfoliation potential. This study provides a comprehensive understanding of $M_3{A}_{2}X$ phases, laying a solid foundation for future experimental synthesis and technological applications.

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• MAX phase compounds
• Density functional theory
• First-principles calculations
• High-throughput calculations