Gravity-induced spontaneous radiation (GISR) treats black holes as general quantum systems with multiple levels and high degeneracy. As results, the intermediate state ofan evaporating black hole is a superposition of various black hole and radiation product combinations with different mass ratios. Since the classical description of a black hole follows from partially tracing out indices of this superposition, the entanglement entropy between the black hole and its radiation products exhibits the first increasing then decreasing feature, aligning with the prediction of Page curve, This work provides a concise introduction to the concept ofGISR, and calculates the entropy variation curve for an initially eight-fold degenerate black hole, demonstrating that the late-time Rabi oscillations are significantly suppressed comparing with its first cycle's increasing-decreasing behaviour.