Abstract: Low cycle fatigue tests were carried out on 316LN steel for the main pipeline of CAP1400 nuclear power unit at room temperature (25 ℃), service temperature (350 ℃), 500 ℃ and 600 ℃, and the cyclic stress response characteristics and hysteresis loops of the steel were obtained. The stable cyclic stress amplitude-strain amplitude curve and strain amplitude-failure reverse number curve were fitted by Ramberg-Osgood model and Manson-Coffin model. The low-cycle fatigue properties of the steel were evaluated by the ASME boilers and pressure vessels code best fitting fatigue curve and design fatigue curve. The results show that the cyclic stress response of 316LN steel consisted of four stages of cyclic hardening, cyclic softening, cyclic stabilization and final failure. The dynamic strain aging phenomenon of 316LN steel was obvious at 500, 600 ℃, but was not obvious at 350 ℃, and no dynamic strain aging occurred at room temperature. Ramberg-Osgood model and Manson-Coffin model could well describe the stable cyclic stress amplitude-strain amplitude and strain amplitude-failure reverse number relationships of 316LN steel, respectively. The fatigue test data of 316LN steel at room temperature and 350 ℃ were higher than the revised best fitting fatigue curve, and the test data with strain adjustment coefficient of 2 or fatigue life adjustment coefficient of 12 were higher than the design fatigue curve, indicating that the low cyclic fatigue properties of the steel met ASME code requirements.