Polyimide has the best combination property among organic polymer materials. Its thermal decomposition temperature will usually be over 500℃ and in -269℃ liquid helium it will not crack. Polyimide has good mechanical property and dielectric properties and unfilled plastic tensile strength will be over 100 MPa, relative dielectric constant will be 3.0-3.5, dielectric loss 10^-3, dielectric strength 100–300 kV/mm. PI film is one of the earliest polyimide product and has been widely used in aerospace, microelectronic devices, display, gas separation, fuel cell and other field and now it has been listed on the most prospective engineer plastic in 21 century. Due to its molecular structure can be cut and its mechanics, thermodynamics, electrical and other properties can be used in wide range of temperature, polyimide will be outstanding as functional material or structural material. Its wide range of application field as been well accepted and acknowledged. Among so many polymers, it is hard to find a certain material can be so widely used and all fields shows such outstanding performances.