Statistical entropy of Kerr-Newman black hole

By using the method of quantum statistics, we directly derive the partition functions of bosonic and fermionic field in Kerr-Newman black hole with axial symmetry. Then via the improved brick-wall method, membrane model, we obtain that the entropy of bosonic and fermionic field in black hole is proportional to the area of horizon. In our result, the stripped term and the divergent logarithmic term no longer exist. The problem that the state density is divergent around the horizon doesn't exist either. We also give the influence of the spining degeneracy of particles on the entropy of black hole. We offer a new simple and direct way of calculating the entropy of different complicated black holes.