A coupling-offset path branch and a high-isolation millimeter-wave phased array antenna based on the same. The high-isolation millimeter-wave phased array antenna includes a plurality of radiating stacked microstrip patch elements, a shielding metal wall, several coupling-offset path branches, a metal ground plane, a feeding network layer, several ports, wherein the first port is excited, energy of the feeding network layer is coupled to a corresponding radiating stacked microstrip patch element through an I-shaped slot, and the energy is transmitted to the second port adjacent to the first port through an inherent coupling path portion; the coupling-offset path branch is introduced to offset the inherent coupling, thus achieving a high-isolation performance between the first port and the second port. By adopting the simple decoupling branch, the invention can achieve a high-isolation effect in a wide band, improve an active standing-wave ratio and a scanning capability of the array antenna.