  The newly discovered Ruddlesden-Popper bilayer La$_3$Ni$_2$O$_7$ reaches an
remarkable superconducting transition temperature $T_c$ = 80 K under a pressure
of above 14 GPa. Here we propose a minimal bilayer two-orbital model of the
high-pressure phase of La$_3$Ni$_2$O$_7$. Our model is constructed with the
Ni-3d$_{x^2-y^2}$, 3d$_{3z^2-r^2}$ orbitals by using Wannier downfolding of the
density functional theory calculations, which captures the key ingredients of
the material, such as band structure and Fermi surface topology. There are two
electron pockets $\alpha$, $\beta$ and one hole pocket $\gamma$ on the Fermi
surface, in which the $\alpha$, $\beta$ pockets show mixing of two orbitals,
while the $\gamma$ pocket is associated with Ni-d$_{3z^2-r^2}$ orbital. The RPA
spin susceptibility reveals a magnetic enhancement associating to the
d$_{3z^2-r^2}$ state. A higher energy model with O-p orbitals is also provided
for further study.
