The frequency of vessel collision is defined as the product of vessel traffic conflicts and causation factors. In the previous studies, the dynamic effects of influencing factors on the ship domain were usually ignored. Using the traffic conflict technique, this study first proposes a dynamic ship domain model and then develops a model to estimate the vessel collision frequency in open seas. Model results show that the most collision risky areas are Niusha Island(24°46.8′N～25°30.0′N), Xiongdi Islet(23°22.8′N～25°49.2′N) and Xiamen Bay Waters(24°08.4′N～24°33.6′N). The collision frequency of the Taiwan Strait is 5.068 7/year, which is very close to the mean value of 4.866 7/year based on 15 years’ historical accident data. Studies indicate that the crossing collision conflict is the major collision type in the Taiwan Strait. In addition, the vessel collision frequency during the nighttime period is slightly bigger than the daylight period. This work not only provides a new method to estimate collision frequency, but also provides a theoretical basis for the quantitative risk assessment of vessel collision in the future.