The invention firstly provides micro-nano fiber and down blended cotton. The micro-nano fiber and down blended cotton is made from, by weight, 15-20 parts of down, 8-12 parts of polypropylene nano fibers and 4-6 parts of polyurethane micro fibers. The invention further provides a making method of the micro-nano fiber and down blended cotton. The making method comprises the steps of pretreatment and electrostatic spinning. The thermal conductivity of the made blended cotton reaches 0.029 W/mK, the specific gravity is only 0.028, the blended cotton is light, dampproof and waterproof, can efficiently prevent parasitism and breeding of acarid for a long time, and will not deform after repeated machine washing or water washing or dry cleaning, and the warmth keeping performance of the blended cotton will not be affected. In brief, according to the blended cotton, the advantages of being resistant to low temperature, good in flexibility, high in adhesive force, high in strength and the like are integrated, moulding and worm damage can be effectively avoided for a long time, corresponding products also have obvious anti-bacterial and odor-resistant functions, and the blended cotton is non-toxic and harmless, low in production cost, high in warmth keeping performance and wide in application prospect.