Abstract: The classification and subregion of reservoir dam risk degree have been given in the study. By analyzing the features of the risk criteria in the civil code of law and the common law systems， it is suggested that the domestic dam risks can be classified into four regions： acceptable risk， tolerable risk， unacceptable risk and extremely high risk. Based on general principles of the risk evaluation， the implications of ALARP principle both in the countries with the common law and in our country are analyzed， and effects and applications of cost effectiveness method and disproportionality ratio method in ALARP principle are stated in this paper. Finally， the principles of dam risk decision-making are establised on a scientific analysis base， which will provide a sound theoretical basis for further research on dam risk and the formulation of dam risk criteria in China.