Atomically dispersed atom catalysts with atomically distributed active metal centers have attracted great attention owing to the maximum atom efficiency and excellent selectivity. Herein, for the first time, we found atomically dispersed Mo atoms can be formed on g-C3N4, and induce its amorphous transformation. This amorphous transformation leads to the formation of strong band tails with remarkably enhancing the absorbance edge of Mo-C3N4 up to 750 nm, resulting in almost whole visible-light range absorption. The formation of new Mo-C and Mo-N bonds due to strong interfacial interaction between atomically dispersed Mo atoms and g-C3N4 provide new electron and hole transport pathways to accelerate the separation of charge carriers. As a result, amorphous Mo/C3N4 (alpha-Mo/C3N4) reveals excellent photoreduction of CO2, yielding CO and H-2 productions of 18 and 37 mu mol g(-1) h(-1) under visible-light illumination (X. > 420 nm), which manifest a remarkable 10.6- and 4-folds enhancement of that over crystalline g-C3N4. This finding provides a conceptually different approach to fabricate high-efficient photocatalyst through the strong interfacial interaction between atomically dispersed metal atoms and host.