Abstract: An anchored ship may drag anchor due to bad weather and hit upstream or downstream bridges. A model is developed based on AASHTO ship-bridge collision model to predict the probability of such a happening. The concepts of the anchor dragging probability and the anchorage probability are introduced into the AASHTO model, and the geometric probability is redefined. The method of probability calculation and the risk grading system are developed. A practical situation where the anchorage site is near a bridge is studied. The measures to reduce the probability of collision accidents are recommended.