Abstract In petrochemical and petroleum refining industries, the hydrogenation technology is widely used. As materials used in key equipment, such as hydrogenation reactors, are subjected simultaneously to the action of hydrogen and high temperature, studies on the material property degradation and remaining life prediction are of very important engineering and academic significance. An in-service test block from the hydrogenation reactor DC101A was divided and tested. Material properties of 2.25Cr–1Mo steel after service of about 10 5 h at the operating pressure of 17.12 MPa and temperature of 427 °C were obtained. Effect of the hydrogen concentration on strength and plasticity of the temper embrittled and de-embrittled 2.25Cr–1Mo steel was studied in the slow strain rate tests (SSRTs). Hydrogen embrittlement susceptibility of the material was evaluated with hydrogen embrittlement index. The safe hydrogen concentration range within which no hydrogen embrittlement occurs was also determined.