Based on the continuum model and independent-particle approximation, this work systematically investigates the synergistic modulation effects of stacking configuration and twist angle on second-harmonic generation (SHG) in twisted bilayer graphene (TBG), twisted monolayer–bilayer graphene (TMBG), twisted double-bilayer graphene (TDBG), and twisted bilayer–trilayer graphene (TBTG). It is found that under single-photon resonance (SPR) or two-photon resonance (TPR) conditions, SHG is significantly enhanced when the incident photon energy matches the van Hove singularity (VHS) band gap. Increasing the number of stacked layers reduces the system symmetry from ${\mathrm{D}}_3$ to ${\mathrm{C}}_3$, effectively switching the dominant SHG response from out-of-plane to in-plane components and enhancing the susceptibility by approximately 50 times, in agreement with experimental values. Reducing the twist angle further enables an order-of-magnitude enhancement of the SHG intensity and a redshift of the resonance energy by increasing the density of states at the VHS while narrowing its band gap. Moreover, polarization-resolved SHG analysis directly reveals the evolution of system symmetry. The results demonstrate that interlayer charge transfer induces an inhomogeneous in-plane electron cloud distribution, breaking the inversion symmetry of the system. This activates the electric dipole response and triggers both the interband Berry curvature and the intraband term of the SHG susceptibility, which constitute the core mechanism driving the SHG response. This work elucidates stacking configuration and twist angle as central tuning degrees of freedom, providing a pathway for designing high-performance, tunable graphene-based nonlinear photonic devices.

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• Nonlinear optics
• Twisted multilayer graphene
• Polarizability
• Optical second-harmonic generation
• Perturbative methods