Past studies have shown that the macroscopic mechanical properties and performance of soil depend on its microstructure essentially. Driving pile into a soft soil would cause a significant change in the internal structure of the soft soil surrounding the pile. The strength and deformation characters are the macroscopic expression of this change. The relationship between soil microstructure and its change of macroscopic mechanical behavior is of great theoretical and practical significance. It can not only reveal the mechanical properties, but also understand its mechanism of effect of driving pile from microcosmic viewpoint. It further provides guidance to the practice. The results provide strong supports to the argument that the microstuctural parameters are the crucial factors of mechanical character by the representative component analysis.