An effective cocatalyst is crucial for the high efficient visible photocatalytic hydrogen generation from formaldehyde. In this study, we develop a novel active Ag₁Pd₁ alloy cocatalyst with selective exposed (1 1 1) facet for the conversion toxic formaldehyde into hydrogen driven by visible light via modulation of the adsorption of HCHO, H₂O molecules and H atom on optimized crystal facet of alloy cocatalyst. The Ag₁Pd₁(1 1 1)/RGO catalyst shows more than two times higher catalytic activity than Ag₁Pd₁(1 0 0)/RGO catalyst under same condition. By taking advantage of the more efficient charge transfer and separation, the prolonged the lifetime of photogenerated electrons has been achieved over (1 1 1) facet AgPd alloy. Our result provides a new insight to develop the active cocatalyst by modulating crystal facet of alloy cocatalyst for hydrogen generation from formaldehyde under visible light irradiation.