In this paper, we propose a new method of using H-2 supply in the atmosphere to increase Sn concentration in a Ge1-xSnx film epitaxially grown on a Ge substrate using MOCVD (metal organic chemical vapor deposition). H-2 supplied in the atmosphere accelerates decomposition of Sn precursors and suppresses surface migration of Sn atoms during epitaxial growth of a Ge1-xSnx film. The proposed method is new and fundamentally different from the existing methods that increase Sn concentration through either crystallizing a-Ge1-xSnx or lowering growth temperature. The proposed method uses H-2 supply in the atmosphere to increase Sn concentration. In order to show the effectiveness of the proposed method, we conducted experiments with varying ratios of supplying H-2 in the atmosphere and epitaxially grew a Ge1-xSnx film on a Ge substrate using MOCVD. MO precursors that we used in our experiments (tertiarybutylgermane and tetraethyl tin) are new and safe. In our experiments, we observed that Sn concentration increased with H-2 supply during growth, while maintaining a high growth rate of a Ge1-xSnx film.