Few-layer ${\mathrm{CrI}}_3$ exhibits thickness-dependent interlayer antiferromagnetic coupling and magnetic-field-induced spin-flip transitions. Although bilayer ${\mathrm{CrI}}_3$ has been extensively studied, the spin dynamics of thicker multilayer structures remain less well understood. In this work, we present systematic simulations and analytical modeling of magnetization reversal and antiferromagnetic resonance modes in bilayer (2L), trilayer (3L), and tetralayer (4L) monoclinic ${\mathrm{CrI}}_3$. By solving coupled Landau-Lifshitz equations using parameters benchmarked against bilayer experimental results, we identify thickness-dependent resonance maps, mode frequencies, and critical fields under both out-of-plane and in-plane magnetic fields. The analytical mode frequencies obtained from linearized equations show good agreement with numerical results. We further demonstrate that antiferromagnetic resonances can be tuned by tens of gigahertz through rotation of the magnetic-field angle. These findings reveal thickness-controlled spin dynamics in van der Waals antiferromagnets and highlight their potential for multistate memory and high-frequency spintronic applications.

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• Magnetization dynamics
• Spin dynamics
• van der Waals systems
• Landau-Lifschitz-Gilbert equation