The physical-mechanical properties of soft soil are largely controlled by the internal microstructure，and the relationship between microstmcture parameters and the engineering properties is essential for microstructure quantitative analysis．Microstructure maps and parameters of soft soil in Nansha area are got by adopting scanning electron microscope(SEM)and image processing technique．Based on the statistic analysis of physical-mechanical indexes and microstructure parameters of soft soil in Na nsha region，the relationship between microstructure parameters and the engineering properties such as compression coeficient，compression modulus，cohesion，and internal friction angle is discussed，and a linear regression equation between microstructure parameters and macro-mechanical properties of soft clay is established．Some beneficial conclusions can act as important evidence for the reliability analysis of soft soil engineering and ground treatment design of soft soil，and guidance on the engineering construction of soft soil in Nansha area．