Abstract: Clayey Silt is a slightly plastic sandy loam the plasticity index（Ip） of which is between 3~10 and its liquefaction occurred in a large area during Tangshan earthquake on July 28, 1976.Formulae with 4 or 5 primary factors for predicting liquefaction potential of clayey silt are presented in this paper. The formulae are derived after analyzing three groups of representative data of clayey silt （involving 126, 166 and 231 points respectively）by using a special computer program prepared by authors.The characteristic of the formulae is associated with a discrimination ratio for liquefaction and non-liquefaction. In addition,they can also be used to choose certain discriminas-tion ratio based on importance of engineering projects.The validity of the formulae is established through checking typical examples from seismic zone with different intensity. A practical application is also mentioned in the end of the paper.