Polar cap patches are common high-density irregularities in the polar cap ionosphere with electron densities of more than twice the background density. Poleward boundary intensifications (PBI) are auroral structures characterized by significantly enhanced brightness of the nightside auroral oval at its poleward boundary. Understanding PBI formation, evolution, and relationship with polar cap plasma is crucial to study the process of polar ionosphere–magnetosphere coupling. In this work, we analyzed the complete PBI generation process triggered by polar cap patches moving to the poleward boundary of the nightside auroral oval, using observational data from the all-sky auroral imager of the Arctic Yellow River Station, the European Incoherent Scatter (EISCAT) radars, and total electron content data from the GPS receivers. The results indicate that high-density plasma moved antisunward and reached the nightside poleward boundary of the auroral oval, markedly enhancing the local auroral intensity and triggering PBI events. When substorms induced a poleward expansion of the nightside auroral oval, EISCAT Svalbard 42 m radars observed high- density plasma structures with high electron and ion temperatures, as well as a decrease of the electron density peak height and an ion upflow, both explained by high-density plasma vertical transport and particle precipitation. This implies that plasma transported from the polar cap region to the nightside auroral oval effectively triggered PBI events that in turn, influenced the plasma characteristics. This analysis clarifies ionosphere–magnetosphere coupling processes in the nightside polar region.