In this paper, a new method to measure the passing capacity of coastal waterway channel is proposed considering service level by computer simulation technique. The passing capacity of coastal waterway channel is first defined by the number of standard ship passing the channel at the required seaport service level. Then the conversion coefficient between the standard ship and other ships is given, which will provide theoretical bases for design, planning and extension of seaport channels. Finally, an application is presented to evaluate the proposed method, and the results show that the larger the ship, the more efficient the waterway channel.