Graphitic carbon nitride (CN) has attracted much attention in photocatalytic fields due to its unique electronic band structure. However, the rapid recombination of photogenerated carriers severely inhibits its catalytic activity. The heterojunction structure has been widely confirmed to significantly improve the photocatalytic activity of CN through the formed interface structure. However, researchers often give attention to the band matching and conductivity of the cocatalyst, while the importance of the interface as a migration channel for photogenerated carriers is often overlooked. In this work, we adopt the strategy of morphology engineering to regulate the morphology of the CN photoactive component so as to achieve the interface optimization of the traditional heterojunction structure. The photocatalytic degradation experiment of rhodamine B shows that compared with the traditional CeO2@CN heterojunction structure, the photocatalytic activity of the interface-optimized CeO2/CN is increased by more than 20%. The following points could be used to explain the improvement of photocatalytic activity: (I) the formed S-scheme heterojunction structure, which inhibits the recombination of useful electrons and holes but expedites the recombination of relatively useless electrons and holes, (II) the increased interface area, which provides more carrier migration channels, and (III) the reduced interface contact resistance, which facilitates the separation and migration of photogenerated carriers. Furthermore, the interface optimization of the traditional Al2O3@CN and Fe2O3@CN heterojunction structures also achieved consistent results. This shows that the strategy in this work is a universal method for interface optimization, which provides potential alternative for further improving the catalytic activity of other heterojunction composites.