One of the bottleneck problems for the realization of the nuclear fusion energy is to choose the key materials in a fusion Tokamak as well as the future reactor. The successful development of fusion power plants is dictated by the successful research of suitable component materials able to resist irradiation by the 14 MeV neutrons as well as the high flux H/He from the deuterium-tritium fusion. Despite many efforts so far, the interaction of H/He with the fusion materials with bcc structure and the blistering mechanism are still not fully understood, making the development of the radiation resistant materials difficult. We thus propose to perform a combined modelling and experimental study on the effect of He, H and particularly their synergy on Fe and W based model systems in order to predict the corresponding microstructural modification. This project brings together French and Chinese expertises on fundamental research of nuclear materials, which is particularly motivated by the fact that both countries are strongly involved in the ITER project. The present scientific project is composed of three main tasks. Task 1 deals with experimental characterizations on Fe and FeCr specimens after multiple-ion-beam irradiations and W samples after He implantation and direct contact with H/He plasma with low-energy and high-flux. Task 2 proceeds simultaneously with the Task 1 and consists in atomistic studies of the properties of diffusion and clustering of He and H with self-defects in Fe and W using complementary techniques. Task 3 deals with direct simulation of our experimental outputs using mesoscopic models parameterized by results of task 2. In practice, the present project is characterized by a close comparison of simulated and experimental data which is useful to validate and improve the various approximations assumed in the theoretical approaches and to explain the atomic-scale origins that drive the experimentally observed data. The synergistic effect of He and H is emphasized as one of the most important objective of this project. All the partners involved in the project have devoted significant effort in the field of nuclear materials from both experimental and modelling sides, characterized by more than 100 publications in international journals including Nature Materials, Physical Review Letters, Physical Review B and Acta Materialia. The computational kinetic Monte Carlo and the rate theory methods in SRMP (CEA-Saclay) and the molecular dynamics and the phase field method in BUAA, the experimental JANNuS in CEA-Saclay and the LPG in BUAA are totally complementary, motivating the present international collaboration.