Abstract: Annular fuel is a new type nuclear fuel for pressurized water reactor (PWR). An annular fuel element has an external cladding corresponding to external coolant channel and an inner cladding corresponding to inner coolant channel, so the PWR whose core is composed of annular fuels has lower core temperature, less fission gas and higher safety allowance. As a new type nuclear fuel and prior to formal operation in the reactor, it’s necessary to test various performances of annular fuel under loss of coolant accident (LOCA) condition out of pile to ensure the safety of reactor core. This paper mainly introduces the experiment results of failure behavior of annular fuel element inner cladding under LOCA, and summarizes the relationship between pressure and temperature when external pressure buckling occurs in the inner cladding, which provides basic data for the safety evaluation and subsequent engineering of annular fuel. The external pressure buckling experiment of the inner cladding of annular fuel element was carried out by means of outer heating of annular electric heating rod in air environment. The results of single rod and the entire results of experiment were analyzed. The experimental buckling pressure was compared with the results calculated by Bresse Bryan formula and numerical simulation results of eigenvalue buckling. The results show that the calculated results of Bresse Bryan formula divided by the safety factor m=2 5 are higher than the experimental results and not conservative enough. The experimental results are distributed between 1/5 and 1/3 of the numerical simulation results of eigenvalue buckling. The data obtained from the experiment can be used in the analysis and calculation of annular fuel.