In this work, the influence of Te atom doping on GaSe1-xTex/MoS2 heterojunctions within the electronic, optical, and photocatalytic behavior are examined by means of first-principles calculations. The outcomes demonstrate that GaSe1-xTex/MoS2 is a van der Waals heterojunction and displays a type-II band alignment, as substantiated by the binding energy and layer separation. Te atom doping can functionally govern the bandgap of GaSe1-xTex/MoS2, and all of them present a progressively decreasing tendency with the increase of the doping concentration, covering a range from 1.28 eV to 0 eV. Additionally, the VBM and CBM in all configurations derive from the contribution of electrons supplied by the Te-p and Mo-d orbitals, respectively. The CDD and W suggest that the electrons in GaSe1-xTex/MoS2 are moved from the GaSe1-xTex to the MoS2 layer, yet the impact of Te doping on the charge distribution at the interface is quite tenuous. Moreover, the increase in Te doping concentration improves the probability of photogenerated electron and hole desynchronization, and the larger VBOs and CBOs in the interlayers of GaSeT0.33/MoS2 and GaSeB0.33/MoS2 lead to a redistribution of electrons, which is conducive to the acceleration of the efficient dissociation of the photogenerated electron-hole pairs. Comparing with the monolayers, the two heterojunctions reveal the relatively wider absorption edge and enhanced light absorption ability in the lower energy visible light range, predicting the potential utilization of both in the fields of photocatalysis and solar energy conversion.