In order to investigate the impact mechanism of explosion fragment size on its collision probability, five typical fragments that often appear in industrial accidents were selected. Taking into account the rotation of the fragments during ejection, a correction factor for collision probability was proposed, and a modified model for fragment collision probability was established. The results of the case analysis show that the maximum ejection distance of the five types of fragments can reach 550-950 m, and the maximum possible ejection distance is distributed between 76-544 m. The ejection distance of CE-type fragments is relatively small, while that of PT-type fragments is relatively large. In addition, under the condition of considering the size of the fragments, increasing the size of the fragments can improve the collision probability. The impact of the fragment size on the collision probability is more significant within a close range of 60 m. When the distance between the fragment and the target exceeds 60 m, the impact of the fragment size on the collision probability can be ignored.