ABSTRACT The existing of hydrogen atom cannot be completely avoided especially in alloy system because of hydrogen atom’s light-weight and susceptive penetration into materials, on the other hand, hydrogen leads to extreme material degraded process not only as chemical corrosion but also as stress-assisted corrosion. In order to get good comprehension which aims to successfully predict hydrogen-induced degraded process and ultimately improve effective usage of “clean energy” and operation security in hydrogen environment, the advanced computational approach such as multiscale modelling [1] is required to consider the material behavior characterization of hydrogen diffusion – mechanics coupling problem in macro-micro scale-bridging, in this first aspect, the relationship between macroscopic effective mechanical and chemical properties and microscopic constitutive material responses are regarded as basic driven force of this multiphysics coupled problem. On the second stage, the extension is shifted into grain boundary as one effect of microstructure which bring feasible modelling for hydrogen-induced grain boundary decohesion, additionally, this microstructural feature also affected local hydrogen balance as one of trapped site within alloy system. As this material degraded process as final stage like switching plasticity – fracture modelling [2], other advanced modelling based on continuum damage aspect is utilized to study hydrogen-induced ductile – brittle transition related to grain boundary effect during chemo – mechanics – damage coupled process. Interests of presentation include the following: • Spatial and temporal scale-bridging for hydrogen diffusion – mechanics problem. • Grain boundary effect on microscopic material hydrogen coupled behaviors. • Fracture ductile – quasi-cleavage transition in hydrogen condition. • Application of aforementioned modelling in aluminium alloy. REFERENCES [1] Tondro, A., Abdolvand, H., On the effects of texture and microstructure on hydrogen transport towards notch tips: A CPFE study, International Journal of Plasticity, Vol. 152: 103234, 2022. [2] Anand, L., Mao, Y., Talamini, B., On modeling fracture of ferritic steels due to hydrogen embrittlement. Journal of the Mechanics and Physics of Solids, Vol. 122: 280-314, 2019.