  The absence of thermal instability in the high/soft state of black hole X-ray
binaries, in disagreement with the standard thin disk theory, is a
long-standing riddle for theoretical astronomers. We have tried to resolve this
question by studying the thermal stability of a thin disk with magnetically
driven winds in the $\dot{M}- \Sigma$ plane. It is found that disk winds can
greatly decrease the disk temperature and thus help the disk become more stable
at a given accretion rate. The critical accretion rate $\dot{M}_{\rm crit}$
corresponding to the thermal instability threshold is increased significantly
in the presence of disk winds. For $\alpha=0.01$ and $B_{\rm \phi}=10B_{\rm
_p}$, the disk is quite stable even for a very weak initial poloidal magnetic
field [$\beta_{\rm p,0}\sim 2000, \beta_{\rm p}=(P_{\rm {gas}}+P_{\rm
rad})/(B_{\rm p}^2/8\pi)$]. But when $B_{\rm \phi}=B_{\rm _p}$ or $B_{\rm
\phi}=0.1B_{\rm _p}$, a somewhat stronger (but still weak) field ($\beta_{\rm
p,0}\sim 200$ or $\beta_{\rm p,0}\sim 20$) is required to make the disk stable.
Nevertheless, despite the great increase of $\dot{M}_{\rm crit}$, the
luminosity threshold corresponding to instability remains almost constant or
even decreases slowly with increasing $\dot{M}_{\rm crit}$ due to the decrease
of gas temperature. The advection and diffusion timescales of the large-scale
magnetic field threading the disk are also investigated in this work. We find
that the advection timescale can be smaller than the diffusion timescale in a
disk with winds, because the disk winds take away most of the gravitational
energy released in the disk, resulting in the decrease of the magnetic
diffusivity $\eta$ and the increase of the diffusion timescale.
