Exhaust noise of marines diesel engines is strongly related to rotating speed. Thus, the active noise control can be realized by composing secondary sound sources with the rotating speed signals as the base frequencies. But the difficulty lies on the determination of the weights of different sound sources. An arithmetic based on calculating the best errorweights is presented to overcome the difficulty. The results indicate that the method can effectively control exhausting noise and trace the change of diesel engines rotating speed. It adapts to the working conditions of marine propelling engines, whose rotating speeds are changing frequently.