  The system of accretion disk and black hole is usually considered as the
central engine of Gamma-ray Bursts (GRBs). It is usually thought that the disk
in the central engine of GRBs is the advection-dominated accretion disk, which
is developed from a massive (mass M_disk) torus at radius r_disk. We find a
positive correlation between the isotropic gamma-ray energy E_iso and duration
(so-called T_90) for GRBs. We interpret this correlation within the
advection-dominated accretion disk model, associating E_iso and T_90 with M_
disk and viscous timescale respectively.
