Van der Waals heterostructures have an incredible potential for the rising self-powered photoelectrochemical photodetectors resulting from their excellent photoelectric conversion functionality and environment friendly interfacial provider transportation. By contemplating the band alignment, structural design, and development optimization, the heterostructures of vertically oriented SnS2 with completely different densities on MoS2 nanosheets are designed and fabricated utilizing a two-step epitaxial development technique. In contrast with SnS2, MoS2, and low-density SnS2/MoS2 heterostructure, the high-density SnS2/MoS2 heterostructure reveals largely enhanced self-powered photodetection performances resembling a large photocurrent density (~932.8 μA cm−2), a superb photoresponsivity (4.66 mA/W), and an ultrafast response/restoration time (3.6/6.4 ms) within the ultraviolet−seen vary. This spectacular enhancement of high-density SnS2/MoS2 photodetector is especially ascribed to the primarily improved cost switch and provider transport of type-II band alignment heterostructure and the environment friendly gentle absorption from the distinctive light-trapping construction. As well as, the photoelectrocatalytic water splitting efficiency of the high-density SnS2/MoS2 heterostructure additionally advantages from the type-II band alignment and the light-trapping construction. This work supplies worthwhile inspiration for the design of two-dimensional optoelectronic and photoelectrochemical units with improved efficiency by the morphology and heterostructure design.