Display omitted •The MoTe2/BAs heterostructure is an excellent candidate for direct Z-scheme photocatalyst.•The band edges fulfil the requirements of photocatalytic water splitting with pH 0 to pH 7.•The light absorption coefficient can reach 5.2 × 104 cm−1 in the range of visible light.•Solar-to-hydrogen efficiency is much higher than other TMDs-based heterostructures. The photocatalytic efficiency of monolayer materials can be greatly improved by constructing two-dimensional van der Waals heterostructures. In this work, the electronic properties and photocatalytic mechanism of the MoTe2/BAs heterostructure with a stable structure are explored via the density functional theory. According to our results, the heterostructure, with a direct band gap value of 0.70 eV, has an intrinsic type-II band alignment that provides indispensable conditions for photocatalytic applications. The built-in electric field formed at the interface accelerates the reorganization of photogenerated holes in MoTe2 and photogenerated electrons in BAs, which results in the photogenerated electrons and holes in the heterostructure accumulate in CB of MoTe2 and VB of BAs, respectively. The spatial separation of photoexcited electrons and holes prolongs the lifespan of carriers and enhances the photocatalytic efficiency of the MoTe2/BAs heterostructure. Besides, these results demonstrate that the heterostructure possesses higher carrier mobility and a higher light absorption coefficient than two monolayers. The MoTe2/BAs heterostructure also has a remarkable solar-to-hydrogen efficiency. These distinguishing features confirm the truth that the MoTe2/BAs heterostructure has promising prospects in the sphere of photocatalysis for water splitting.