  The hard to soft state transition of the outbursts in X-ray binaries (XRBs)
is triggered by the rising of the mass accretion rate due to the disk
instability. In order to explain the observed correlation between the hard
X-ray transition luminosity and the soft X-ray peak luminosity in the soft
state, we construct a magnetic disk-outflow model for the state transition in
XRBs. We assume that the large-scale magnetic field in the outer thin disk is
formed through inverse cascade of small-scale dynamo generated field, and it is
then advected by the inner advection dominated accretion flow (ADAF), which
accelerates a fraction of the gas into the outflows. During the outbursts, the
heating front moves inwards, and the field strength at the heating front of the
outer disk is proportional to the accretion rate of the disk. Much angular
momentum of the inner ADAF is carried away by the outflows for a stronger
magnetic field, which leads to a high radial velocity of the ADAF. This makes
the critical mass accretion rate of the ADAF increases with the field strength,
and it therefore leads to a correlation between transition luminosity and the
peak luminosity in the thermal state. We found that the values of the viscosity
parameter $\alpha$ of the neutron star XRBs are systematically higher for those
of the black hole (BH) XRBs ($\alpha\sim 0.05-0.15$ for BHs, and $\alpha\sim
0.15-0.4$ for neutron stars). Our model predicts the transition luminosity may
be higher than the peak luminosity provided $\alpha$ is sufficiently high,
which is able to explain a substantial fraction of outbursts in BHXRBs not
reaching the thermally dominant accretion state.
