An analytical method was developed to detect the molecular weight of cotton cellulose. This method uses gel permeation chromatography coupled with multi-angle static laser light scattering（GPC-MALS） and adds ionic liquid to dissolve the cotton. The separation of GPC does not require high mobile phase，no gradient drenching，simple experimental operation，good reproducibility，fast test speed，and has many features that other chromatography does not have. MALS measures the light scattering intensity of the sample at each angle. The sample is separated by the column. The RI detector measures the concentration of the eluent. This allows the molecular weights of individual slices to be calculated. By combining GPC and MALS，it not only separates different sets of fractions，but also measures the root-mean-square radius，molecular weights and their distributions of different sets of fractions，and does not require standard samples and standard curves. Therefore，it is widely used in the fields of macromolecular research，biochemistry and reaction kinetics. After the samples were treated with NaOH base，cotton cellulose was dissolved by adding N，N-dimethylacetamide（DMAc） to 1-butyl-3-methylimidazolium acetate（BmimAc） ionic liquid，and then the ionic liquid type test was changed，and af

ter comparing the four ionic liquids methods for dissolving cotton cellulose，it was concluded that BmimAc ionic liquid was the most effective. Various temperatures were also tried to dissolve cotton cellulose，and the dissolved solution was passed through 0.22 μm PTFE filters and then used directly for GPC-MALS to detect its molecular weight. The results showed that cotton cellulose still could not be dissolved at 40 ℃ for a long time； the time needed to dissolve cotton cellulose gradually decreased from 50 ℃ to 80 ℃，and the molecular weight was about 2.2×10

4

，and the inaccuracies were all within 5%，so the results were reliable； the molecular weight of cotton cellulose dissolved at 90 ℃ was 6.634×10

4

，thermal glycosylation at the reducing end is suggested to occur under the neat pyrolysis conditions. The molecular weight distribution of the cellulose was slightly shifted to the high molecular weight region after heat treatment. In summary，the new method for the detection of molecular weight of cotton cellulose by multi-angle laser light scattering coupled with gel permeation chromatography using BmimAc as an additive has the advantages of simple preparation，mild dissolution conditions，high detection precision，fast detection and low consumption，which overcomes the problems of traditional methods，such as the inability to measure absolute molecular weight and the difficulty of finding structurally similar standards.