  Beyond 14GPa of pressure, bi-layered La$_3$Ni$_2$O$_7$ was recently found to
develop strong superconductivity above the liquid nitrogen boiling temperature.
An immediate essential question is the pressure-induced qualitative change of
electronic structure that enables the exciting high-temperature
superconductivity. We investigate this timely question via a numerical
multi-scale derivation of effective many-body physics. At the atomic scale, we
first clarify that the system has a strong charge transfer nature with
itinerant carriers residing mainly in the in-plane oxygen between spin-1
Ni$^{2+}$ ions. We then elucidate in eV- and sub-eV-scale the key physical
effect of the applied pressure: It induces a cupratelike electronic structure
through partially screening the Ni spin from 1 to 1/2. This suggests a
high-temperature superconductivity in La$_3$Ni$_2$O$_7$ with microscopic
mechanism and ($d$-wave) symmetry similar to that in the cuprates.
