  We study the asymptotic symmetry group(ASG) of the near horizon geometry of
extreme Kerr black hole through the effective action approach developed in
1007.1031. By requiring a finite boundary effective action, we derive a new set
of asymptotic Killing vectors and boundary conditions, which are much more
relaxed than the ones proposed in 0907.0303, and still allow a copy of
conformal group as its ASG. In the covariant formalism, the asymptotic charges
are finite, with the corresponding central charge vanishing. By using the
quasi-local charge and introducing a plausible cut-off, we find that the higher
order terms of the asymptotic Killing vectors, which could not be determined
through the effective action approach, contribute to the central charge as
well. We also show that the boundary conditions suggested in 0809.4266 lead to
a divergent first order boundary effective action.
