Intrinsic High Chern Numbers in Two-Dimensional <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">M</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow>

Despite sharing a common lattice structure, monolayer M_{2}X_{2} compounds realize quantum anomalous Hall phases with distinct Chern numbers, a striking phenomenon that has not been fully explored. Combining first-principles calculations with symmetry analysis and tight-binding models, we identify two generic band-inversion mechanisms governed by the orbital composition and symmetry representations of 3d states near the Fermi level. When d_{xz} and d_{yz} orbitals dominate, a doubly degenerate Γ-point inversion yields C=1; otherwise, inversions occur along Γ-X and Γ-Y at four C_{4}-related momenta, whose Berry-curvature contributions add to give C=2, distinct from scenarios relying on multiple band inversions at a single k point. The same mechanism consistently explains related two-dimensional systems, including LiFeSe, KTiSb, MgFeP, and Janus M_{2}X_{2} derivatives. The mechanism provides practical guidance for screening and engineering tunable high-Chern-number insulators.