Abstract: The cyclic high temperature and high pressure water corrosion system was used to simulate the water chemical condition of primary circuit of pressurized water reactor (PWR) for corrosion test of SiC/SiC_f composite cladding tube. The corrosion behavior of SiC/SiC_f composite cladding tube was analyzed through mass loss and micro morphology after corrosion. The results show that the SiC/SiC_f composite cladding tube experienced mass increase stage, mass acceleration loss stage, mass stability loss stage and mass loss slowing down stage during the corrosion process. During the initial mass increase stage of corrosion, silicon-rich oxide films covered on the surface of cellular crystals, slowing the corrosion dissolution of the cladding tube. In the accelerated mass loss stage, corrosion dissolution and oxide shedding accelerated corrosion of cladding tube. In the mass stability loss stage, the corrosion dissolution and the formation of oxides on the specimen surface played a balance role. In the mass loss slowing down stage, the dense oxides on the specimen surface significantly alleviated the corrosion dissolution and reduced the mass loss rate after corrosion.