Dredger is the most widely used dredging equipment in dredging engineering，and its productivity directly affects the efficiency of the dredging process. This paper establishes a prediction model of dredger productivity by using rough sets theory，and the model validation experiment is carried out for the working condition of cutter suction dredger excavating cohesive soil. According to the real ship data and empirical research results，soil parameters and soil grade are used to characterize the soil change，and the productivity prediction results under the two methods are compared. The results show that the productivity errors of the both methods are less than 10%，and the method of establishing productivity prediction model using rough set technology is feasible. The predicted value is calculated based on soil grade is much closer to the actual value.