The preparation method of the thin film is as follows: The polyamide acid solution is deposited into the film, and after stretching, the High-temperature amide. The film is yellow transparent, relative density 1.39~1.45, has outstanding high temperature resistance, radiation resistance, chemical corrosion resistance and electrical insulation performance, can be used in 250~280℃ air for a long time. The vitrification temperatures were 280 ℃ (Upilex R), 385℃ (Kapton) and 500 ℃ (Upilex S). 20 ℃ when the tensile strength of 200mpa,200℃ is greater than 100MPa. Especially suitable for flexible printed circuit board substrate and a variety of high-temperature electrical insulation materials.