Statistical entropy of a charged black hole

By using the method of quantum statistics, we derive 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 impr oved brickwall method. When we choose a proper parameter in our results, we can obtain that the entropy of a black-hole is proportional to the area of the horizon. In our result, the neglected term and the divergent logarithm ic term given in the original brickwall method do not exist. We avoid the d ifficulty 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.