Abstract: An integer programming model is built to optimize bauxite transshipment fleet for minimum annual total charter costs. The optimization is under the constraints of inconsistency of the demand for transshipment, the limitation of port storage capacity and the tidal time window. The model is applied to the transshipment line from Yantai port to Taoer river harbor, Binzhou for verification. The model is solved with the differential evolution algorithm. The results suggest that every ship to do 13 voyages a month is appropriate. It is seen that the freight has most significant impact on reasonable size of the fleet and the shipper should choose ahead of transshipment schedule, which will alleviate the pressure on port storage and, meantime, keep the charter cost minimum.