Fabrication of semi-solid LY11 alloy by SIMA (strain-induced melt activation) technique was studied, effects of process parameters, height reduction (), isothermal temperature (Ti) and holding time, on grain size, fractal dimension and grain size distribution were investigated quantitatively. The results show that the height reduction has a great effect on microstructure evolution. Grain growth and spheroidization are promoted with increasing the isothermal temperature or elongating the holding time. Grain size has a Gaussian distribution for all samples. In the adjacent domain of peak point, counts of grains reduced and grain size increased with the decreasing of height reduction, the increasing of isothermal temperature and holding time. Pretreatment condition, i.e. cold or hot deformation, has important effects on microstructure evolution, and deformation of samples is a necessary step in SIMA process.