  Reconsideration of the Regge-Wheeler equation is processed by using the
Painlev\'{e} coordinate and "good" timelier to define the initial time. We find
that: the Regge-Wheeler equation could has positive imaginary frequency.
Because the Regge-Wheeler equation is the odd (angular) perturbation to the
Schwarzschild black hole, the conclusion is that the Schwarzschild black hole
is unstable with respect to the rotating perturbation.
