Development of multispectral perfect light absorbers for applications in biological sensing, spectroscopic imaging, and selective thermal emitters is urgently required. Unfortunately, current multispectral absorbers are typically only based on a combination of fundamental resonances of multiple resonators using the design concepts of a coplanar superunit structure or multiple vertically stacked layers, which does not introduce new resonances while such structures are difficult to fabricate. In this work, a type of quad-spectral absorber formed by a double-layer stacked resonant structure is presented and demonstrated. Numerical simulations show that the suggested structure can achieve near 100% absorption at four frequency bands. The quad-spectral absorption results from excitation of two sets consisting of the fundamental mode and third-order resonance of the designed structure. The suggested device is insensitive to the polarization of the incident light due to the high degree of symmetry of the resonance structure. Device parameters are investigated to further explore the physical origin of the quad-spectral absorption. Moreover, it is revealed that the number of resonance peaks can be further increased by employing one more layer.