Referring to Phase I project of 300,000 DWT navigation channel to Lianyungang Port,we analyze the causes from the aspects of external factors,human factors,technical factors and management factors in view of the common quality defects existed in dredging works,and put forward the preventive measures such as increasing the equipment input,innovating dredging technology,adjusting construction plans,strengthening personnel training and project management,etc.Good results are achieved in the Phase I project of 300,000 DWT navigation channel to Lianyungang Port.