  We present a broad band spectral analysis of the black hole binary GX~339-4
with NuSTAR and Swift using high density reflection model. The observations
were taken when the source was in low flux hard states (LF) during the
outbursts in 2013 and 2015, and in a very high flux soft state (HF) in 2015.
The high density reflection model can explain its LF spectra with no
requirement for an additional low temperature thermal component. This model
enables us to constrain the density in the disc surface of GX~339-4 in
different flux states. The disc density in the LF state is $\log(n_{\rm e}/$
cm$^{-3})\approx21$, 100 times higher than the density in the HF state
($\log(n_{\rm e}/$ cm$^{-3})=18.93^{+0.12}_{-0.16}$). A close-to-solar iron
abundance is obtained by modelling the LF and HF broad band spectra with
variable density reflection model ($Z_{\rm Fe}=1.50^{+0.12}_{-0.04}Z_{\odot}$
and $Z_{\rm Fe}=1.05^{+0.17}_{-0.15}Z_{\odot}$ respectively).
