The invention relates to a method for expanding excavation of a large-diameter shield tunnel for subway station construction through a pile arch wall support. The method comprises the steps that a single-hole double-track tunnel of a station portion is used as a part of the station structure, pipe segment structures at the bottom and the top of a shield are reserved, and a bottom longitudinal beam, a middle partition wall and a top longitudinal beam of the station structure are constructed; the remaining station structures on the two sides of the shield tunnel are formed through expanding excavation, an air flue at the end of the station is used as a working plane, expanding excavation is carried out on the two sides of the large-diameter shield tunnel by the adoption of a hole pile method, the pipe segment structures on the two sides of the shield are removed in the expanding excavation process, and meanwhile the connection measure between a cast-in-place structure and the remaining pipe segments is taken to form the single-layer double-span side platform subway station. The method for expanding excavation of the large-diameter shield tunnel for subway station construction through the pile arch wall support has the advantages of being definite in stress, reasonable in conversion, convenient to construct and the like.