According to the requirements of the Code of Design for Breakwater and Revetment，for the sloping dikes on the scoured foundation，large stones of the underwater prisms should be thrown on small stones with a thickness of not less than 0.5 m or the geotextile soft mattress. For sandy coasts with partially exposed rocks，the geotextile soft mattress is easily punctured in part and cannot be used，and it is also difficult to meet the design working life of up to 50 a. Furthermore，there is no strict international standard on the filter calculation of pre-laid gravels，and no strict theoretical basis for gravel thickness. In view of these problems，combined with the filter design principles from China and foreign countries，this paper elaborates the filter design of the sloping dike bottom by adopting the strict filter principle and geometrically stable filter principle，which better makes up for the design deficiencies in the international standard.