The invention discloses a preparation method of a cellulose-based composite photocatalytic material and application thereof. Cellulose is dissolved in ionic liquid under microwave radiation and is subjected to functional modification; then, a prepared photocatalyst precursor solution is added into the modified cellulose solution, reaction is performed under the condition of microwave-assisted ionic liquid to prepare the cellulose composite material, and the photocatalytic degradation performance of the composite material to a methyl orange solution is tested under a high-voltage mercury lamp. The prepared cellulose-based composite photocatalytic material can have higher photocatalytic activity without high-temperature calcination, the activity of a photocatalyst is improved, and the methyl orange degradation rate under the condition of catalytic degradation time of 80 minutes is as high as 98.31%. The composite material can be repeatedly utilized.