Polyimide fiber, also known as P84 fiber, is a heat-resistant fiber with excellent high temperature resistance. At 300℃ for 100 h, the strength retention rate is 50%, the elongation is reduced by 5% ~ 10%, and the exposure rate is 250 H, strength retention rate of 45%, excellent dimensional stability at 275℃, no melting, glass temperature of 315℃, only release a little harmful gas when decomposition. It can run continuously at 260℃ and the instantaneous working temperature can reach 280℃.