The work aims to design a glue coating device for document bags and make the glue coating mechanism adapt to the gluing sealing of document bags of different sizes and the complex working conditions. Based on the dynamic principle and the substitution principle of mechanical system of TRIZ theory, the glue coating mechanism of the document bag was designed. The glue coating device for document bag sealing could accurately apply glue to different sizes of document bags, thus eliminating the problem of leakage caused by artificial glue and greatly improving the production efficiency and safety. By TRIZ theory, the problems of high cost, low production efficiency and inaccurate sealing of existing glue coating devices for different sizes of documents are solved.