The invention relates to a plasma processing apparatus and a method for adjusting a process rate of a marginal area of a substrate. The plasma processing apparatus comprises a cavity, a pedestal arranged in the cavity, a gas spay header arranged at the top of the cavity, a lower electrode arranged in the pedestal, a focusing ring arranged around the substrate, an edge electrode, and a phase shifter. To be specific, an electrostatic chuck is arranged above the pedestal; and a substrate is arranged above the electrostatic chuck. The gas spay header is used as an upper electrode; and process gas enters the cavity through the gas spay header. The lower electrode is connected with a first radio frequency power supply. The edge electrode approaches the edge area of the substrate and is connected with a second radio frequency power supply. And the phase shifter is connected with the first radio frequency power supply and the second radio frequency power supply. According to the invention, the edge effect can be effectively compensated; and phenomena of arc discharging and sparking due to the short distance between voltages applied to the central zone and the edge zone of the substrate can be avoided.