Abstract: The object Kinetic Monte Carlo (OKMC) method is an effective tool that can simulate evolution of microstructures in irradiated materials. It can deal with defect diffusion and interaction between defects while accounting for the spatial correlation of defects. It has a sufficiently large space-time scale, making it possible to directly compare with experimental observations. In this paper, the OKMC method and model were introduced in detail. Then the application of OKMC in the simulations of irradiated materials was demonstrated by a few examples, including calculation of sink strength, cascade annealing simulation, embrittlement of reactor pressure steels, effect of impurities on the evolution of microstructure, and void lattice formation. At last, advantages and disadvantages of the OKMC method and the issues needed to be addressed in future were discussed. The results show that OKMC method has the characteristics of accuracy, flexibility and large space-time scale, and can be applied effectively in the field of irradiation simulation. Future development of OKMC method should focus on parallelization of the algorithm, applications to complex systems and combination with other methods with different scales.