Graphitic carbon nitride (g-C₃N₄) has become an attractive visible-light-responsive photocatalyst because of its semiconductor polymer compositions and easy-modulated band structure. However, the bulk g-C₃N₄ photocatalyst has the low separation efficiency of photogenerated carriers and unsatisfied surface catalytic performance, which leads to poor photocatalytic performance. As for this, MgTi₂O₅ with high chemical stability, wide band gap and negative conduction band was used as a suitable platform for coupling with g-C₃N₄ to enhance charge separation and promoted the photoactivity. Different from common approaches, here, we propose an innovative method to construct g-C₃N₄/MgTi₂O₅ nanocomposites featuring "0 + 1 > 1" magnification effect to improve g-C₃N₄ photocatalytic performance under visible light irradiation. Additionally, compositing metal oxides of MgTi₂O₅ with g-C₃N₄ has proven to be a proper strategy to accelerate surface catalytic reactions in g-C₃N₄, and the photoinduced carriers were modulated to maintain thermodynamic equilibrium, which convincingly promotes the photocatalytic activity. The photocatalytic performance of the nanocomposites was measured by hydrogen production and CO₂ reduction under visible light. The developed g-C₃N₄/MgTi₂O₅ nanocomposites with a 5 wt.% MgTi₂O₅ exhibits the highest H₂ and CO yield under visible light and excellent stability compare to the other MgTi₂O₅ contents in composites. According to surface photo-voltage spectra, electrochemical CO₂ reduction, photoluminescence, etc. The superior performance can be related to an enhanced electron lifetime, the promoted charge transfer and the increased electronic separation property of g-C₃N₄. Our work provides an approach to overcome the defect of pure g-C₃N₄, which accesses to composite with the second component matched well.