The results of hydrogen determination in aluminum melt by using an instrument HYSCAN II show that both hydrogen porosities and hydrogen content in Al alloys possess the character of heredity. The heredity of hydrogen in porosities is a portion of the heredity of hydrogen in Al alloys. Hydrogen existing in different forms possesses different heredity efficiency. Accordingly, a concept of "heredity efficiency" has been proposed. The effect of factors such as cooling rate and melting condition on the heredity has been studied, as well as the mechanism of heredity.