The invention relates to a method for reducing the characteristic dimension of a photoresist pattern, which comprises the following steps of: (1) providing a wafer with a substrate layer, and forming the photoresist pattern on the substrate layer; (2) adopting a first gas, applying a microwave flow to the first gas to produce a plasma, and downstream etching the wafer to reduce the characteristic dimension of the photoresist pattern. The invention has the advantages that the wafer can be isotropically etched by using the microwave flow to produce the plasma, so that the reduction in the effective height of the photoresist pattern is little when the characteristic dimension of the photoresist pattern is reduced; the photoresist can provide better protection to a lower layer in subsequent processes, and the quality of the product is ensured. In general, the microwave flow of a photoresist removing chamber can be used for etching, the photoresist removing chamber is equipment with low construction cost, the utilization ratio of the equipment is increased, and the production cost can be reduced.