Zirconium alloys used as fuel claddings in water-cooled nuclear reactors generally serve in a harsh environment of high-temperature high-pressure water and strong neutron irradiation. Nb is known to play an important role in improving the corrosion resistance of zirconium alloys. Therefore, studying the microstructural changes and its effect on the corrosion behavior of zirconium alloys with different Nb contents before and after irradiation can provide a basis for the design of advanced zirconium alloys. In this work, Zr-0.75Sn-0.35Fe-0.15Cr-xNb (x=0, 1.0, wt%) alloys were prepared and irradiated with 2 MeV He_⁺ at 300 ℃. The effects of irradiation on the microstructure and corrosion behavior of the alloys were investigated by using scanning electron microscope and transmission electron microscope. The corrosion environment was 360℃/18.6 MPa/0.01 M LiOH aqueous solution. The results revealed that the number, average size and crystal structure of the second phase particles in Zr-0.75Sn-0.35Fe-0.15Cr-xNb alloys changed with the increase of Nb content prior to irradiation. After He_⁺ irradiation to 1 dpa, however, a large number of He bubbles and -type dislocation loops were induced in the radiation damage peak region in the alloys. To some extent, addition of Nb can affect the number of He bubbles and dislocation loops and elemental diffusion from the second phase particles. The corrosion results showed that He_⁺ irradiation or addition of 1.0wt% Nb could accelerate the corrosion of Zr-0.75Sn-0.35Fe-0.15Cr alloy, but the irradiation could reduce the acceleration effect of Nb on the corrosion of Zr-0.75Sn-0.35Fe-0.15Cr alloy.