The invention relates to a method for preparing a functional nano fibrous membrane by a multi-component consolute single-step method, which comprises the following steps: (1) preparing solution in which the volume ratio of dimethyl acetamide DMAc to methanol is 40-50:50-60, and adding a methanol sweetener and a membrane penetrating agent for co-dissolution; and (2) adopting a smoothed needle as acapillary for jetting small flows to connect a high pressure generator for electrostatic spinning, controlling flow rate of spinning solution by a micro injector pump, and receiving fiber. The preparation method is simple; and the prepared nano fibrous membrane can simply prepare functional membrane products with functions of administration, nutrition supplementation and absorption, convenient daily sanitation and the like.