Abstract: Lixiahe district,where the Huaiyan expressway runs,has broadly distribution of high water-content and high compressive ancient lagoon facies soft soil.The soil has engineering low-grade properties.There is a close relationship between its engineering properties and the development mechanism of Lixiahe lagoon.In this paper,it starts from changes of the sedimentary environment and local geology,points out the development mechanism of Lixiahe lagoon facies soft soil,based on the general development model of lagoon.After these,it analyzes the engineering properties of typical lagoon facies soft soil from Huaiyan expressway,and estimates the distribution of lagoon facies soft soil based on the vertical changes of its engineering properties.Finally,the paper gives the relationship between its engineering properties and growth mechanism.