With the addition of SiC particle and copper-mould spray casting, the heterogeneous nucleation ability of AZ91 magnesium alloy is enhanced under high cooing condition and thus the grain refinement of sub-rapid solidified microstructure was fabricated. Then, the effect of annealing temperature (320℃、370℃ and 400℃) on the dynamic solid solution process of divorce eutectic β-Mg17Al12 phase was investigated. As for the spray casted AZ91+1wt%SiC after annealing for 320℃+2h, incomplete solid solution occurs, accompanied by the preservation of initial irregular petal-like morphology and the formation of tiny fringes. After annealing at 370℃, the disappearing rate of β phase is accelerated except for the residual of few grain boundary region. With further increasing temperature to 400℃, a single solid solution of α-Mg phase forms and its morphology transits into fine polygonal grain. Grain refinement is more obvious after the addition of 2wt%SiC, which promotes the process of solid solution due to the shortened atomic diffusion distance. The hardness of copper-mould spray casted magnesium alloy is enhanced by 28.75% due to the addition of SiC and increase of grain refinement, whereas a decline trend appears after solid solution treatment because of the reduction of grain boundary.