Statistical entropy of a charged black hole

By using the method of quantum statistics, it is derived directly the partition functions of the bosonic and the fermionic field in the charged-black-hole space-time. The statistical entropy of a black-hole is obtained by an improved brick wall method. When it is chosen a proper parameter in these results, it can be obtained that the entropy of a black-hole is proportional to the area of the horizon. In the results, the neglected term and the divergent logarithmic term given in the original brick wall method do no exist. It is avoided the difficulty in solving the wave equation of the scalar and Dirac fields, and offer a simple and direct way of studying the entropy of the black hole