  The classical first law of thermodynamic for Kerr-Newmann black hole (KNBH)
is generalized to that in quantum form on event horizon. Then four quantum
conservation laws on the KNBH equilibrium radiation process are derived, and
Bekenstein-Hawking's relation S=A/4 is recovered. It can be argued that the
classical entropy of black hole arise from the quantum entropy of field quanta
or quasi-particles inside the hole.
