Polyimide is non-toxic, can be used to make tableware and medical devices, and can withstand thousands of times of disinfection. Polyimide is one of the organic polymer materials with the best comprehensive properties. It can resist high temperature above 400℃, and has no obvious melting point in the long-term use temperature range of -200~300℃. Its dielectric constant is 4.0 at 103 Hz and its dielectric loss is only 0.004~0.007, so it belongs to F-H insulating materials. As a special engineering material, it has been widely used in aviation, aerospace, microelectronics, nanometer, liquid crystal, separation membrane, laser and other fields. In 1960s, all countries listed the research, development and utilization of polyimide as one of the most promising engineering plastics in 2 1 century.