Graphitic carbon nitride (g-C3N4) has been widely used to improve photoelectrochemical (PEC) activity owing to its outstanding photoresponse and strength. In this study, g-C3N4 hollow tubes decorated with SnO2 quantum dots were prepared by combining hydrothermal and post-annealing approaches. In particular, different characterization techniques such as Fourier transform infrared, photoluminescence, ultraviolet–visible, and X-ray photoelectron spectroscopies were employed to investigate the electrical and optical behaviors of the samples. The prepared samples exhibited considerable photoresponse and excellent PEC performance, producing hydrogen. Furthermore, the heterostructures among SnO2 and g-C3N4 encouraged carrier separation, improving the PEC ability. In addition, the applied voltage showed numerous effects on generating charge carriers for the anodes in a 0.1 M sodium hydroxide electrolyte. Therefore, the proposed approach is simple and effective and can be used to enhance the performance of the PEC activity.