We report ALMA observations of the dust continuum and {cii} emission of the host galaxy of J0439+1634, a gravitationally lensed quasar at $z=6.5$. Gravitational lensing boosts the source-plane resolution to $sim0farcs15$ $(sim0.8text{ kpc})$. The lensing model derived from the ALMA data is consistent with the fiducial model in citet{fan19} based on {it HST} imaging. The host galaxy of J0439+1634 can be well-fitted by a Sersic profile consistent with an exponential disk, both in the far-infrared (FIR) continuum and the {cii} emission. The overall magnification is $4.53pm0.05$ for the continuum and $3.44pm0.05$ for the {cii} line. The host galaxy of J0439+1634 is a compact ultra-luminous infrared galaxy, with a total star formation rate (SFR) of $1.56times10^{3}M_odot/text{year}$ after correcting for lensing and an effective radius of $0.74$ kpc. The resolved regions in J0439+1634 follow the ``{cii} deficit, where the {cii}-to-FIR ratio decreases with FIR surface brightness. The reconstructed velocity field of J0439+1634 appears to be rotation-like. The maximum line-of-sight rotation velocity of 130 km/s at a radius of 2 kpc. However, our data cannot be fit by an axisymmetric thin rotating disk, and the inclination of the rotation axis, $i$, remains unconstrained. We estimate the dynamical mass of the host galaxy to be $7.9sin^{-2}(i)times10^{9}M_odot$. J0439+1634 is likely to have a high gas-mass fraction and an oversized SMBH compared to local relations. The SFR of J0439+1634 reaches the maximum possible values, and the SFR surface density is close to the highest value seen in any star-forming galaxy currently known in the universe.
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