I will give a purely quantum information perspective for the Island formula. In a quantum system when the state of a subset is totally encoded in the state of another subset, the way we compute the reduced density matrix and related entropy quantities will change essentially, which result in a new island formula in quantum systems, which we conjecture to be the same island formula in gravity recently proposed to rescue the unitarity for black hole evaporation. The new perspective help us better understand the entanglement wedge cross-section in island phases in the context of partial entanglement entropy.