Abstract: The microstructure of in-situ reactive spray formed 7075+XTiC (the volume fraction X=0,1.15%, 1.73%, 2.91%, 4.48%, 5.95%) after heat treatment at 610℃ and 620℃ for 30min were observed using SEM. The grain size was measured by a mean linear intercept method to analyze the effect of different volume fractions of in-situ TiC particles on the semi-solid microstrucrure of spray formed 7075 alloy. It was shown that at 610℃ the pinning effect was significant when the volume fraction of in-situ TiC particles was up to 2.91%, which made micro-structures of the alloy keep as-spray formed characteristics and could meet the requirement of subsequent semi-solid processing. If that of in-situ TiC particles exceeded 2.91%, the grain size was further decreased, but the number of dispersoids and particles at grain boundaries evidently increased with net-shaped distribution. When that was less than 2.91%, the grain grew abnormally at local areas, resulting in the homogenization reduction of grain structure.