The rational construction of a high-efficiency step- scheme heterojunctions is an effective strategy to accelerate the photocatalytic H₂. Unfortunately, the variant energy-level matching between two different semiconductor confers limited the photocatalytic performance. Herein, a newfangled graphitic-carbon nitride (g-C₃N₄) based isotype step-scheme heterojunction, which consists of sulfur-doped and defective active sites in one microstructural unit, is successfully developed by in-situ polymerizing N,N-dimethyl-formamide (DMF) and urea, accompanied by sulfur (S) powder. Therein, the polymerization between the amino groups of DMF and the amide group of urea endows the formation of rich defects. The propulsive integration of S-dopants contributes to the excellent fluffiness and dispersibility of lamellar g-C₃N₄. Moreover, the developed heterojunction exhibits a significantly enlarged surface area, thus leading to the more exposed catalytically active sites. Most importantly, the simultaneous introduction of S-doping and defects in the units of g-C₃N₄ also results in a significant improvement in the separation, transfer and recombination efficiency of photo-excited electron-hole pairs. Therefore, the resulting isotype step-scheme heterojunction possesses a superior photocatalytic H₂ evolution activity in comparison with pristine g-C₃N₄. The newly afforded metal-free isotype step-scheme heterojunction in this work will supply a new insight into coupling strategies of heteroatoms doping and defect engineering for various photocatalytic systems.