We have aleady developed many large programs in the field of port & harbour structures. Each large program consists of a lot of subprograms. We can see common subprograms in many large programs. Once we make common subprograms and arrange them, we can use them when we make a new large program. It is very convenient for us to have such common programs in view of promoting automatic design.
　The structure of common subprograms must be ruled strictly to be used in every large program. We, first, have analyzed the strurcture of port & harbour design and second, we have tried to find what part of it is common subprogram. We can find 136 ones. Third, we have ruled the content of common subprograms in detail.