According to the engineering geological investigation in the north of Jiangsu province, the southern transition zone in Xuyi that is between the foothill and the plain shows the typical close hillbillabong physiognomy. In the billabong, the special softsoil is founded and differentiates from the common coastal soft soil. And its engineering geological properties are comparatively special. In this paper, the formation characteristics and the distribution rules are discussed. Meanwhile the mineral and chemical components, physical and mechanical properties, swelling—shrinkage properties, the swelling properties and the CBR values of the compacted soil are all analyzed. It is indicated that besides the characteristics of the common softsoil, its clay mineral and particle contents are high, and its shrinkage is evident. Because the majority of the clay particles aggregate, the swelling property of its undisturbed specimens is not very evident. But when Xuyi softsoil is compacted, it has the prominent swelling property. If this special softsoil can not be treated correctly, it would bring the stabilitylost of the embankment, the asymmetric settlement and the craze cracking of the road surface. So it should be concerned.