Abstract: Tungsten (W) and its alloys are the most prospective plasma facing materials (PFMs) in future fusion reactors. The service performance of W and its alloys directly affects the safety of fusion reactors in long-term service. Irradiation-induced microstructure evolution of W and its alloys leads to the irradiation embrittlement phenomenon, which is always the key factor limiting its engineering application. In this paper, based on the molecular dynamics calculation results, the cluster dynamics model was improved for modeling the irradiation-induced microstructural evolution behavior of materials. A more complete physical model to describe the generation behavior of radiation defects in materials was adopted, and the influence of the generation process of radiation defects in W matrix on the microstructural evolution behavior was explored. The simulation results show that the defect clusters directly generated by cascade collisions induced by high energy primary displacement atom (PKA) are the most important nucleation mechanism in the evolution of dislocation loops and cavities in W. The diffusion behavior of interstitial clusters caused by heterogeneous nucleation has an important influence on the growth behavior of dislocation loops, resulting in the appearance of sub-spikes and step morphology in the size distribution of dislocation loops.