Ternary composites Ni2P/g-C3N4/ZnIn2S4 were synthesized via a hydrothermal method, and their catalytic performance were evaluated by photoreduction of CO2. Kinds of characterizations (XRD, SEM, TEM, XPS, UV-vis, EIS, and PL) were applied to investigate the morphology, crystal structure, surface chemical states, band structure and photoelectric property of the composites. The results showed that the heterostructure with intense contact was constructed successfully via the facet engineering. Besides, the introduction of Ni2P and g-C3N4 could improve the band structure of photocatalysts, shorten the transmission distance of electrons and inhibit the recombination of photo-induced carriers effectively. Therefore, compared with pure g-C3N4 and binary composites g-C3N4/ZnIn2S4, ternary composites Ni2P/g-C3N4/ZnIn2S4 exhibited higher catalytic activity. Among Ni2P/g-C3N4/ZnIn2S4 composites, CNZ5 (Ni2P:g-C3N4:ZnIn2S4=1:5:7) revealed the optimal CO2 photoreduction efficiency, in which the yield amount of CH4, CH3OH, and HCOOH was 114.72 μmol·h?1·g?1, 17.38 μmol·h?1·g?1, and 20.15 μmol·h?1·g?1, respectively. In addition, the CO2 photoreduction mechanism was obtained by the application of in-situ DRIFTS, and the intermediates of HCO3- and HCOOH were found during the reaction process.