Abstract: Influences of composition and proportion of high and low temperature melt on the primary Si phase refinement of hypereutectic Al-Si alloy during melt mixing treatment were investigated. The long lasting effectiveness and re-melting stability of the melt mixing treatment were also discussed. It is found that the larger the difference of Si content between the high and low temperature melts before mixing, the smaller the grain size of primary Si phase in the mixing alloy. Mixing Al-30%Si melt and Al-10%Si malt in a weight proportion of 1∶1 could obtain the optimal refining effect that the primny Si phase size was 36.9 μm. The validity of the mixing melt was less than 5 min when holding outside the furnace directly, while holding at 830 ℃ inside the furnace, the size of primary Si was about 36 μm within 100 min. Melt mixing treatment had a good first time re-melting stability, but its refinement effect gradually lost with the prologation of second time re-melting.