The invention relates to a method for ultrasound assisted preparation of uniform rod-like nano-cellulose, relating to a preparation method of rod-like nano-cellulose and aiming to solve the problem of high production cost in the existing method for preparation of the uniform rod-like nano-cellulose via homogenization under ultrasonic and high-pressure conditions. The method comprises the following steps of: preparing sodium hypochlorite/sodium hydroxide solution, adding the solution into microcrystalline cellulose for moisten expansion, carrying out ultrasound-assisted dispersion after moisten expansion, carrying out acid hydrolysis of mixture of white flocculent cellulose and water after dispersion, centrifugally separating after acid hydrolysis, centrifugally washing with deionized water, carrying out ultrasound-assisted fragmentation after washing, diluting with deionized water, and finally refrigerating and freeze-drying sequentially, thereby obtaining the uniform rod-like nano-cellulose. The invention has the advantages that: 1, the production cost is reduced; and 2, the preparation process is simple and can be operated easily. The method is mainly applied in preparation of the uniform rod-like nano-cellulose.