  We explore thermal X-ray iron line emission from the galactic X-ray binary GX
339-4 in the off state, using the models of the advection dominated accretion
flow (ADAF) without or with outflows. The equivalent widths of hydrogen-like
and helium-like thermal iron lines are calculated with different model
parameters including viscosity parameter $\alpha$, mass accretion rate at the
outer radius of the ADAF $\dot{m}_{\rm out}$ and outflow strength parameter
$p$. Our calculations show that the equivalent widths of thermal iron lines
emitted from the pure ADAF, i.e., the ADAF without outflows, should be very
small, assuming a solar metallicity for the accreting gas in the accretion
flow. Strong thermal iron lines are expected to be emitted from the ADAF with
relatively strong outflows. {For reasonable choice of parameters, the total
equivalent width of the He-like and H-like thermal iron lines reaches to
$\gtrsim 500$ eV for accreting gas with solar metallicity. The observation of
strong thermal X-ray lines from GX 339-4 at the off state may give a clue to
the accretion mode of the source and provide evidence for the presence of
outflows/winds in the accretion flow around the black hole in GX 339-4. It is
found that the values of $\dot{m}_{\rm out}$ and $p$ are degenerate, i.e., the
observed X-ray continuum spectrum can be fairly well reproduced with different
sets of the parameters $\dot{m}_{\rm out}$ and $p$. Such {degeneracy} can be
broken when the thermal X-ray line emission data is available. We also compare
our results with those in the previous similar work.}
