Statistical entropy of Reissner-Nordstroem black hole

By using the method of quantum statistics, we directly derive the partition function of bosonic and fermionic field in Reissner-Nordstroem black hole. It is the same as the one obtained by solving wave equation approximately. Then via the improved brick-wall method, membrane model, 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 don't exist any more. The problem that the state density is divergent around the horizon doesn't exist either. We also give the influence factor of the spining degeneracy of various particles on the entropy of black hole. In the whole process, we do not take any approximation. We offer a new simple and direct way of calculating the entropy of different complicated black holes