Abstract: The paper describes the compaction characteristics of clayey soil. In view of the basic conception that the optimum degree of saturation Srop under various compaction energy is constant, and the optimum moisture content of the standard compaction energy is approximately the plastic limit, a method by using plastic limit wP and optimum saturation for estimation of the maximum dry density is presented as follows:γdmax=Srop·G3/G3wp+Sropwhere G3 is the specific gravity of the soil particles,wP is the plastic limit.Methods of determining the compaction criterion of clayey soil are discussed and the coefficient of construction m is introduced and demonstrated with suggestion value 0.95~0.97 for medium and low dams, and 0.97~0.99 for high dams.