The invention discloses a method for preparing a wood-plastic composite 3D printing material from recycled plant cellulose. The method comprises the steps of: 1) performing air drying and dust removal on a recycled plant fiber raw material, then performing crushing and screening, then pretreating a waste raw material containing plant fibers by using alkali, then washing the fiber raw material to be neutral, then drying the fiber raw material until the fiber water ratio is less than or equal to 4%, and performing crushing and screening; 2) preparing a mixed solution of acetic acid and chitosan, wherein the content of the chitosan in the mixed solution is 5-55wt%, the content of the acetic acid is 0.5-3.5wt%, and the pH value of the mixed solution is controlled to be 4.5-6.5; and 3) premixing the fiber raw material powder after crushing with PLA at a temperature of 75-90 DEG C for 3-8min, then spraying the mixed solution of acetic acid and chitosan into a compound system, performing stirring for 7-16min, then preparing a filiform material, thereby obtaining the wood-plastic composite 3D printing material. The method disclosed by the invention provides a new raw material for the 3D printing material, and moreover, by the method, environmental pollution can be reduced, wastes can be changed into valuables, and the economic benefit and social benefit are improved.