The connection between shear strength and micro-structure of solidified soil is to be done. However, most of the literature is only qualitative analysis between macro and micro. The purpose of this paper is to get the macro-micro relationship. The dredger fill is solidified by the different curing agent mixed with fly ash, and the shear strength index is measured by the direct shear test. The microscopic images are obtained by using Scanning Electron Microscope (SEM). The image is dealt with by using Image-Pro Plus (IPP), and the micro-structure parameters are deduced that include mean equivalent particle diameter Dp, mean equivalent pore diameter Db and plane void ratio e. The research shows that there is no linear relation between the internal friction angle and the micro-structure parameters; The cohesion has a good linear relation with three micro-structure parameters; Compared with the other two microstructural parameters, the function of the plane void ratio on the cohesion is greater.