Abstract: Flat Dilatometer Test(DMT)is a relatively new in-situ test technique,which has been widely used in the geotechnical engineering investigation and design,but it is seldom applied to the evaluation of soft soil foundation improvement.DMT was used in the evaluation of an expressway’s soft foundation improvement by different techniques.The traits and applicability of DMT in the evaluation of soft soil improvement were discussed.The results of this research show that the soil’s undrained shear strength and constrained modulus deducted from DMT can directly reflect the variation of the mechanical properties of foundation soils before and after treatment,DMT has the features of near continuity and sensitivity to the variety of soil properties.It is reliable to employ DMT in the analysis and evaluation of foundation improvement.