The Relation Between Technique of Conformal Flat and Damour-Ruffini-Zhao's Method

The relation between the technique of conformal flat and Damour-Ruffini-Zhao's method is investigated in this paper. It is pointed out that the two methods give the same results when the metric has the form $g_{\alpha\beta=0},$ with $\alpha=0,1$ and $\beta=2,3$. It is indicated that the two methods are not equivalent for general case.