Abstract: A system for fast measuring hydrogen content in aluminum alloy melt was developed based on dynamic measurement of hydrogen partial pressure and Sieviet's law. The system consists of a changing volume vacuum chamber unit, a changing volume driven unit and a data acquisition and processing unit. The hydrogen content in aluminum alloy melt was gotten by monitoring the real pressure and computing the theoretical pressure in the vacuum chamber, calculating the difference between the two pressures, finding the hydrogen partial pressure, and using the empirical formula. The system is fast and accurate in testing, simple in operating, and low in testing cost.