Disclosed are a plasma reactor for ultra-high aspect ratio etching and an etching method therefor, wherein the plasma reactor comprises: a reaction chamber inside which a reaction space is formed; a base disposed at the bottom of the reaction space and configured for supporting a to-be-processed substrate; a gas showerhead disposed at the top inside the reaction chamber; wherein a first radio frequency power supply outputs a radio frequency power with a first frequency to the base or the gas showerhead so as to form and maintain plasma in the reaction chamber; and a second radio frequency power supply which outputs a radio frequency power with a second frequency to the base so as to control the ion energy incident to the base; wherein the first frequency is not less than 4 MHz, and the second frequency is not less than 10 KHz but not more than 300 KHz.