Abstract: Chinese port investment theory and practice is still in the infancy, and are unable to adapt the actual needs of port sustainable development. The managerial flexibility involved in the contingent investment can be described and valued by expansive real options, an integrated value function model for the investment of port expansion is established，which reflects characteristics of the high degree uncertainty of port investment, in pursuit of maximum investment return, and port phased investment. The model is set up to calculate the optimal capacity with numerical techniques when the target investment return index of the port is mainly concerned. Finally, with a practical example, the results show that the model has the significantly practical applications.