Abstract: Hydrogen can cause hydrogen defects such as white spots and cracks in steel, which will seriously reduce the mechanical properties of materials. The method of hydrogen filling in gas phase was adopted, and the steel samples were respectively held for 1 h at the temperature of 200-900 ℃. Under the condition that hydrogen-induced cracks appear on the surface of the sample for the first time, the critical temperatures for cracks in steel samples of three different components were explored. The hydrogen content at the critical temperature was determined to be 1.98×10^-6g·g^-1, 2.34×10^-6g·g^-1and 2.65×10^-6g·g^-1, respectively. The results provide theoretical support for the quality control of on-site steel and the formulation of slow cooling dehydrogenation process.