Abstract: Double electrolytic cell electrochemistry hydrogen permeation test was conducted on two grade 690 MPa medium Mn steels with different composition in queched state and tempered state. The effects of chemical composition and heat treatment condition of the tested steel, and hydrogen charging current on the hydrogen diffusion behavior were analyzed. The results show that the microstructures of two tested steels after quenching both consisted of lath martensite, and reverted austenite was observed after tempering at 650℃; the reverted austenite content of the tested steel adding alloying elements of Cu, N and Cr was higher and lath martensitic was finer. The difference of the hydrogen diffusion behavior of the two quenched tested steels was not obvious, but after tempering, the hydrogen permeation rate and hydrogen apparent diffusion coefficient in the tested steel added with alloying elements were both relatively small, and the hydrogen permeation time was relatively long. The hydrogen charging current had a little effect on the hydrogen permeation rate of the quenched tested steel, but had a great effect on the tempered tested steel. With the increase of hydrogen charging current, the hydrogen permeation rate and the hydrogen apparent diffusion coefficient of the tempered tested steel both increased, hydrogen permeation time shortened.