The rational design and construction of p-n heterojunctions were deemed as an efficient strategy for promoting the separation and migration of photogenerated electron-hole pairs. Here, a facile in-situ deposition process was applied to develop a novel dual-functional Ag2O quantum dot/ZnIn2S4 nanosheet (AO/ZIS) composite photocatalyst, which assisted to the uniform distribution of Ag2O quantum dots on the surfaces of ZnIn2S4 nanosheets for the fabrication of the unique p-n heterostructure. The as-prepared AO/ZIS hybrids presented significantly enhanced photocatalytic performance for both hydrogen generation and tetracycline hydrochloride (TCH) decomposition. The results indicated that sample AO/ZIS-2 possessed the highest photocatalytic H-2 production capacity (2334.19 mu mol center dot g(-1)) and TCH photodegradation rate (1.62 x 10(-2) min(-1)), which were 3.38 and 3.82 times as high as those of bare ZnIn2S4. Meanwhile, based on a series of characterization analysis, it could be determined that the increased surface area, enhanced spectral absorption and the fabrication of p-n heterojunction with the interface electric field were primarily responsible for the wonderful photocatalytic activities. Ultimately, the possible energy band transition after contact and photocatalytic mechanism were elucidated according to the ESR and Mott-Schottky results. It is predictable that our work will provide some inspiration for exploring other p-n heterojunctions with excellent performances.