Abstract: Hydrogen-induced cracking (HIC) is one of the most common defects in the welding of ultra-high strength steels (UHSS). The level of varying crack susceptibility in different zones is related to the hydrogen diffusion behavior across different zones of the welded joint, which is influenced by the microstructural transformation within the welded joint. This study employed an improved microphotography technique to investigate the diffusion patterns of hydrogen in the welded joint when using the ER110S-G welding material and the 11Cr-7Ni martensitic welding material for welding Q1100 UHSS. Hydrogen micro-printing over 72 hours was used to trace the final distribution of hydrogen in the welded joint. The reasons for the differences of hydrogen distribution in the welded joint between the ER110S-G and 11Cr-7Ni welding materials were explored. The findings indicate that when using the ER110S-G welding material, hydrogen predominantly accumulates in the weld metal (WM) and heat-affected zone (HAZ). In contrast, the 11Cr-7Ni welding material mainly accumulates hydrogen in the WM. The lower martensitic transformation temperature of the 11Cr-7Ni welding material inhibits diffusion of hydrogen from the WM to the HAZ, thereby reducing the hydrogen concentration in the HAZ. This study provides novel insights into the relationship between the WM phase transformation behavior of UHSS and the hydrogen embrittlement tendency in different zones of the welded joint.