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We explore thermal X-ray iron line emission from the galactic X-ray binary GX339-4 in the off state, using the models of the advection dominated accretionflow (ADAF) without or with outflows. The equivalent widths of hydrogen-likeand helium-like thermal iron lines are calculated with different modelparameters including viscosity parameter $\alpha$, mass accretion rate at theouter radius of the ADAF $\dot{m}_{\rm out}$ and outflow strength parameter$p$. Our calculations show that the equivalent widths of thermal iron linesemitted from the pure ADAF, i.e., the ADAF without outflows, should be verysmall, assuming a solar metallicity for the accreting gas in the accretionflow. Strong thermal iron lines are expected to be emitted from the ADAF withrelatively strong outflows. {For reasonable choice of parameters, the totalequivalent width of the He-like and H-like thermal iron lines reaches to$\gtrsim 500$ eV for accreting gas with solar metallicity. The observation ofstrong thermal X-ray lines from GX 339-4 at the off state may give a clue tothe accretion mode of the source and provide evidence for the presence ofoutflows/winds in the accretion flow around the black hole in GX 339-4. It isfound that the values of $\dot{m}_{\rm out}$ and $p$ are degenerate, i.e., theobserved X-ray continuum spectrum can be fairly well reproduced with differentsets of the parameters $\dot{m}_{\rm out}$ and $p$. Such {degeneracy} can bebroken when the thermal X-ray line emission data is available. We also compareour results with those in the previous similar work.}

Thermal X-ray iron line emission from the advection dominated accretion flow in the galactic binary GX 339-4