The loosening process of bolts is divided into two stages: material loosening period and structural loosening period.Looseness during material loosening period is mainly caused by plastic deformation.In order to study the factors affecting the bolt looseness during the loosening of material under impact load, an accurate bolting model was established.Then the Yamamoto method and Sopwith method were used to verify the validity of the model.Finally, a finite element simulation analysis was carried out to study the influences of the impact load magnitude, the initial pre-tightening force, the friction coefficient between the threaded mating surfaces and the initial gap of thread on the bolt loosening during material loosening period under impact load.The results show that the smaller the impact load magnitude and the smaller the initial gap of thread during loosening period, the less likely the bolt looseness will occur; there is an initial preload value or range, and there is also a friction coefficient value or range between the thread meshing surfaces to make the bolt loose the least likely to happen.