Ultra-high-strength secondary hardening martensitic steel achieves precipitation strengthening and improved toughness during the tempering process. Abundant precipitates can act as hydrogen traps, reducing the hydrogen diffusivity, which provides significant application potential in the manufacturing of hydrogen embrittlement resistant structural components, such as bolts, connecting rods, gears, and shafts. It is necessary to investigate the types, scales, and distribution of carbide precipitates during the tempering process, as well as their interaction mechanisms with hydrogen, in order to find optimum tempering conditions for improved hydrogen embrittlement resistance. This study employs in-situ slow strain rate tests under hydrogen charging and electrochemical hydrogen permeation measurements to investigate the influences of microstructural features on hydrogen embrittlement susceptibility and hydrogen diffusion behavior. Additionally, fracture initiation mechanisms in the fracture surface region are studied through combined Electron Backscatter Diffraction and Electron Channeling Contrast Imaging. Experimental results indicate that the types of carbides changes from ε-carbides→M3C →M2C during the tempering temperatures of 400-650 Celsius degree, leading to differences in hydrogen embrittlement sensitivity and hydrogen diffusion rates. Effective control of carbide types and morphology can significantly influence the material's hydrogen embrittlement resistance. The current research elucidates the interconnections between microstructure features and fracture initiation mechanisms, providing support for mitigating susceptibility to hydrogen embrittlement through the control of carbide precipitation behavior.