Problems in vacuum sealed molding casting Al-Si alloy were described based on characteristics of the vacuum sealed molding and cast Al-Si alloy properties,including Al-Si alloy easier to oxidation and inspiration,high difference value of hydrogen solubility in between liquid aluminum and castings,slow heat radiation of vacuum sealed molding and high solidification contraction of Al-Si alloy.It is adopted to successfully produce Al-Si alloy high voltage switch by keeping the raw material properly to make a good preparation before melting and rapidly melting to decrease pouring temperature and time and raising cooling velocity and exhaust degree in cavity,fully refining as well as adopting tilting pouring.