<p>Broadband and efficient sound insulation is widely desired in engineering. Linear acoustic metamaterials (LAMs) can break the mass law for sound insulation, but this benefit occurs within narrow bands, meanwhile, the valleys in LAMs greatly reduce the insulation effect. To overcome these disadvantages, this paper proposes a nonlinear acoustic metamaterial (NAM) plate that can significantly broaden the sound insulation via strongly nonlinear interaction. We establish the nonlinear finite element model of the NAM plate and systematically investigate its nonlinear structure-sound dynamics. Relative to the LAM plate with the same mass, the NAM plate can avoid insulation valleys and broaden the bandwidth for highly efficient insulation by about 64%. We confirm that the broadband effect is attributed to the super-equivalent mass from bi-oscillator strong nonlinear interaction. Experimental devices and samples are fabricated to demonstrate the broadband effect enabled by NAM plate. This paper opens novel way for sound insulation. The modeling and design methods also provide guidance for studying this topic.</p>