This present work investigate the hydrogen content in Al-12Si alloy at different holding temperatures of 993K, 1023K, and 1053K and under different ambient relative humidity 30%RH, 50%RH, 80%RH. The relationship of the hydrogen content with atmosphere relative humidity and the reaction time was investigated. A HYSCAN II analyzer was used to evaluate the hydrogen content in aluminum melts. The experimental results show that the hydrogen content increased with the holding temperature and the relative humidity. At the temperature 1053K, the hydrogen content has an inverse change. The hydrogen content is more depend on the liquid structure than physical mass transfer and chemical reaction because of the sudden change in liquid microstructure. A group of kinetic regression equations of the hydrogen absorption in Al-12Si melts was obtained.