Abstract: A measuring method taking views of hydrogen behaviours under microscope is applied to study the redistributive and bubbling-up course of the residual diffusible hydrogen in the grey iron weldments welded with both the homogenous and the heterogenous electrodes. Because the flaky graphite can not only store the hydrogen but also block the hydrogen to diffuse forward, the amounts of the residual diffusible hydrogen which can come into the HAZ of the grey iron joint is very small, and so the influence of the hydrogen on the cold cracking tendency of the HAZ of grey iron joint is little too.