The invention discloses a method for prolonging milk fresh-keeping time by utilizing CO2 micro-nano bubbles, which belongs to the technical field of milk fresh-keeping. The method comprises the following steps: checking and accepting raw milk: checking and accepting the raw milk in three aspects of sensory examination, physical and chemical indexes and microbiological examination; mechanically filtering the milk: filtering the milk by using milk filter paper under the pressure condition of 50kPa; mixing the milk and CO2 and then introducing a mixture into a micro-nano bubble device, and forming a milk-CO2 micro-nano bubble mixed system; and storing the milk-CO2 micro-nano bubble mixed system obtained in the above step 3 in a milk storage tank which is cleaned, disinfected and sterilized inadvance. The problems of microbial pollution and the like in the transportation process from a pasture to a processing factory in the traditional milk processing process are solved by utilizing the small bubble size, high solubility, high adsorption rate, low rising speed in milk and the bacteriostatic action of CO2 of the micro-nano bubbles, and the effect of better prolonging the fresh-keepingperiod of the milk is achieved.