Abstract: Two-dimensional materials have attracted much attention due to their unique properties, and heterojunction is an important means to reduce the band gap and promote effective charge separation. Therefore, the construction of two-dimensional heterostructure is a key way to improve the photocatalytic properties of materials. First-principles calculations can be used to effectively design suitable heterostructure. The electronic and optical properties of g-C₃N₄/xBlueP (x=1, 2, 3) heterojunction with different structures have been studied by first-principles calculations. The results show that the g-C₃N₄/2BlueP heterojunction has the most suitable band edge positions, wide optical response range and good light absorption capacity. The type transformation of g-C₃N₄/2BlueP heterojunction can be realized by applying appropriate biaxial strain, which solves the problem of high electron-hole recombination of type I heterojunction. This is particularly valuable for achieving efficient photogenerated charge separation. The strain-regulated g-C₃N₄/2BlueP heterojunction is found to significantly increase the absorbance of the visible light, compared with the light absorption properties of the two constituent materials.