When a heavy-duty cutter suction dredger is used for rock channel dredging,the minimum dredging depth and width are under restrictions.We carry out the computing method of confirming the minimum dredging depth and width.We introduce the calculation method of the minimum depth and the width under different wave conditions，which is based on standard specification and geometry size of the dredger.We work out the minimum dredging depth and width by this method in a project example.The method is proved to be useful.