Preparation method of flame-retardant cellulose derivative

The invention discloses a preparation method of a flame-retardant cellulose derivative. The method comprises the following steps of 1. dissolving cellulose in an ionic liquid to obtain a homogeneous cellulose solution, the cellulose being one of wood pulp, cotton pulp and hemicelluloses; 2. dissolving a flame retardant in the ionic liquid to obtain a homogeneous flame retardant solution, the flame retardant being a phosphorus-based flame retardant; and 3. mixing the cellulose solution, the flame retardant solution and triethylamine, heating, stirring and post-processing to obtain a cellulose derivative with a flame-retardant property. The flame-retardant cellulose derivative obtained by the method contains no halogen, is environment-friendly and has no pollution. LOI value of the flame-retardant cellulose derivative reaches a national standard of flame-retardant materials.