Abstract: The performance of polyimide towards β-irradiation of tritium is studied by TG-DTA,IR,and mechanical behavior tests.The non-irradiated polyimide reveals no weight loss till 553 ℃,anddecomposes at 600 ℃ with ammonia as the main released gaseous component.After one year irradiation by tritium β~-particles,the IR spectrum of polyimide remains almost unchanged as a whole,except small variation in intensity for some of its peaks.Small changes in its mechanical characters are observed due probably to the radiation degradation.The concentration of nitrogen in the residual gas(over) the stockpile is slightly higher than in the feeding tritium gas,indicating the degradation of polyimide is negligibly small.The results show that polyimide has good resistance to tritium irradiation,and is suitable to be used as a sealing material in tritium technology.