Conventional second-harmonic generation (SHG) interference, such as nonlinear magneto-optical effects, typically requires magnetism and strong spin-orbit coupling, limiting its occurrence to rare materials, narrow frequency ranges, and restrictive tunability. Challenging this assumption, we demonstrate through symmetry analysis and first-principles calculations that SHG interference can arise purely from crystal symmetry without magnetism or spin-orbit coupling. We show a stable and giant crystal SHG interference occurs universally in $C_{3v}$-symmetric nonmagnetic materials within the broad nonresonant regime. The proposed interference mechanism transcends traditional limitations, offering a transformative potential for distinguishing twinned structures, enabling nonlinear optical diode effects, and advancing electric-field-controlled SHG technologies.

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• First-principles calculations
• Nonlinear optical materials
• Nonlinear optical susceptibility
• Second order nonlinear optical processes
• Hexagonal boron nitride
• Photodiodes
• Chiral symmetry