The invention discloses a cellulose gum, and a preparation method and an application thereof. The preparation method of the cellulose gum comprises the following steps: (1) stirring, mixing and reacting cellulose powder and an alkalizing agent in the presence of water and isopropyl alcohol to obtain alkalized cellulose, wherein a mass ratio of the water to the cellulose powder is (1.50-3.80):1, and a mass ratio of the alkalizing agent to the cellulose powder is (0.60-0.70):1; and (2) carrying out an etherification reaction on the alkalized cellulose obtained in step (1) in the presence of an etherifying agent to obtain the cellulose gum, wherein a mass ratio of the alkalizing agent to the cellulose powder is (0.70-0.80):1. The food grade cellulose gum prepared in the invention can ensure that the protein centrifuging precipitation rate of an acidic dairy beverage is equal to or less than 1.5% and the acidic dairy beverage can be stored for 21 d without layering when applied to the acidic dairy beverage as a food additive, and has very good milk protein suspending and stabilizing effects.