The paper demonstrates that the distribution law of ships to port obeys the binomial distribution by mathematical statistics,the mathematical and physical meanings are clear,and afford to the objective law.The binomial distribution matches the truth.The Poisson distribution is a similar method of the binomial distribution.This paper validates the similarity of the two distributions by examples,expounds the feature of Poisson distribution,and points out the condition of using Poisson distribution instead of the binomial distribution by comparing the two calculation methods.This paper also establishes the discriminant of the rational number of berths,introduces the method and step of calculation of reasonable number of berths by the queuing theory,and applies them to practical cases.