TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: In the step (i) of raw material processing, using benzyl alcohol extraction to remove impurities in lignocellulosic raw material, where the impurities are terpene compound, fats, waxes, sugar, tannin, polyphenol substance, pigment, watersoluble polysaccharide, and salt. The lignocellulosic raw material impurity removal using benzyl alcohol extraction specifically comprises weighing 10 g wood powder in an electronic scale, adding benzyl alcohol to extract, placing in a Soxhlet extractor, weighing 100 ml toluene and 50 ml ethanol and mixing in volume ratio of 2:1 to obtain a solution, extracting wood powder for 6 hours, removing impurities, then extracting, using ethanol to wash, filtering and drying at room temperature until it is completely dried. The step (ii) of chemical treatment comprises placing dried wood powder in 400 ml distilled water, weighing 3.7 g sodium chlorite and adding into the solution, then taking 3 ml glacial acetic acid and adding into the solution, processing the solution in a water bath at 75 degrees C for 1 hour, continuously stirring, adding into a to be sealed beaker, then repeating process for 6 times, each time adding 3.7 g sodium chlorite and 3 ml glacial acetic acid, processing, washing using distilled water, adjusting pH value of the solution to neutral using potassium hydroxide solution with the concentration of 6%, adding wood powder in potassium hydroxide solution, placing in a water bath for 2 hours at 90 degrees C, removing hemicellulose, in order to completely remove lignin, reprocessing wood powder by sodium chlorite for 3 times, in order to completely remove hemicellulose, reprocessing using potassium hydroxide, where the concentration changes of from 6% to 3%, processing using 1% hydrochloric acid at 80 degrees C for 2 hours to obtain the purified cellulose fiber. The step (iii) of mechanical treatment comprises processing the obtained cellulose fiber into solution to prepare nano cellulose by four different methods: (i) pre-processing cellulose fiber, grinding in a grinding machine for 30 minutes to obtain cellulose micro cellulose, crushing using cell crusher and ultrasonicating for 60 minutes to obtain nano cellulose, (ii) grinding cellulose fiber after pre-processing in a grinding machine for 30 minutes to obtain cellulose micro cellulose, homogenizing for 8 times in a high pressure homogenizer to obtain nano cellulose, (iii) grinding cellulose fiber in a grinding machine for 60 minutes to obtain nano cellulose, or (iv) pre-processing cellulose fiber, crushing using a cell crusher for 60 minutes, then homogenizing for 8 times in a high pressure homogenizer to obtain nano cellulose. The step (iv) of preparing nano cellulose film comprises carrying out mechanical processing method to obtain nano cellulose suspension, stirring for 1 hour at normal temperature, using 400 ml 1% nano cellulose suspension liquid, starting vacuum pump, filtering, completely draining the distilled water, removing nano-cellulose film, placing between two pieces of glass plate, drying for 24 hours in a vacuum drying box, taking out to obtain nano cellulose film. The preparation of nano cellulose/polylactic acid composite film material by mixing/impregnation comprises drying polylactic acid and nano cellulose for more than 24 hours in a vacuum drying box, weighing 4.95 g polylactic acid and 50 ml dichloromethane and placing in a beaker, heating, placing the beaker on the magnetic stirrer, stirring at normal temperature for 2 hours until the poly lactic acid particles are completely dissolved, adding 0.05g freeze-dried nano-cellulose in dichloromethane solvent, ultrasonicating for 10 minutes, adding nano-cellulose after ultrasonic dispersion into the polylactic acid solution, stirring for 12 hours at room temperature, fully dispersing nano cellulose in the polylactic acid, and then casting the mixed solution on the iron plate, drying iron plate for 12 hours at normal temperature, then drying for 24 hours in a vacuum drying tank of 60 degrees C, uncovering film, so as to obtain the nano cellulose/poly-lactic acid composite film, where the nano cellulose content is 1%; or the preparation of nano cellulose/polylactic acid composite film material by mixing/impregnation comprises drying polylactic acid for more than 24 hours in a vacuum drying tank of 45 degrees C, weighing 5 g polylactic acid and 50 ml dichloromethane and placing into a beaker, heating the beaker, then placing on a magnetic stirrer, stirring at normal temperature until the polylactic acid particles are completely dissolved, after 2 hours, dipping prepared nano-cellulose film in acid solution for 8 hours, taking out and drying for 12 hours at normal temperature, drying for 24 hours in a vacuum drying tank of 60 degrees C to obtain nano cellulose/poly-lactic acid composite film, where the content of nano cellulose is 58%.