The computer simulation of squeeze casting of Al-Si binary alloys were studied by modelling of solidification and calculating of temperature changes of the mould and casting in comparison with gravity casting. The calculated interface heat transfer coefficients at the mould/cast in gravity casting were 0.055, 0.022 and 0.017㎈/sec ㎠ ℃ for hypoeutectic, neareutectic and hypereutectic Al-Si alloy, respectively. These are due to different behaviour of the formation of air gab that affected from growth morphology and thermal conductivity of constituted phases. As squeeze casting, The calculated values were 0.6, 0.3 and 0.15㎈/sec ㎠ ℃ for hypoeutectic, neareutectic and hypereutectic Al-Si alloy, respectively. Pressurization made remarkably improved the contact condition between the mould and casting as eliminated air gab. It resulted in increasing of interface heat transfer coefficient by one order magnitude or more as pressurized. The critical transition value of interface heat transfer coefficient from gravity casing to squeeze casting on Al-Si binary alloys was 0.06㎈/㎠ sec ℃.