Comparing with the traditional earth rock cofferdam，the steel pile cofferdam has advantages of small cross-section and higher retaining water head when it is used on the soft clay foundation.But due to the lack of systemic theoretical calculation，the empirical or semi-empirical design and construction is low in safety assurance rate，therefore its application in engineering is limited.Combining with an engineering example，we present the main indicators and calculation methods which may affect the stability of the steel-pile cofferdam，and the result may serve as reference for the design and construction of similar projects.