Although lead halide perovskites are demonstrated to be promising photocatalysts for hydrogen evolution from hydrogen halide splitting, it still remains challenging to fabricate efficient and stable catalysts. Here MoS₂ nanoflowers with abundant active sites are assembled with methylammonium lead iodide (MAPbI₃) microcrystals to form a new heterostructure. Its hydrogen evolution rate can reach up to about 30 000 μmol g^–1 h^–1, which is more than 1000-fold higher than pristine MAPbI₃ under visible light irradiation (λ ≥ 420 nm). Importantly, the solar HI splitting efficiency reaches 7.35%, one of the highest efficiencies so far. The introduction of MoS₂ with proper band alignment and unsaturated species can efficiently promote the charge separation and afford more active sites for H₂ production. This finding not only provides a highly efficient and stable photocatalyst for hydrogen evolution but also offers a useful modification strategy on lead halide perovskites.