Graphitic carbon nitride (g-C3N4) has been considered as one of the most promising photocatalysts for solar energy conversion. However, the intrinsic drawbacks of insufficient visible-light absorption and poor charge separation efficiency seriously limit its practical applications in visible light photocatalytic hydrogen evolution. In this work, a facile one-step strategy was proposed to construct a novel porous defect-modified graphitic carbon nitride (P-DCN) via thermal polymerization of a freeze-dried crystalline mixture containing dicyandiamide (DCDA) and ammonium chloride (NH4Cl) under nitrogen atmosphere, in which both porous feature and two types of defects (cyano group and nitrogen vacancy) were simultaneously introduced into g-C3N4 framework. Results show that the as-synthesized P-DCN Exhibits 26 times higher hydrogen evolution rate (HER) under visible light irradiation than bulk g-C3N4, reaching 20.9 mu mol h(-1). In combination of porous and defective characteristics, P-DCN even demonstrates 2.0 and 1.8 folds higher HER than highly active porous graphitic carbon nitride (P-CN) and defect-modified g-C3N4 (DCN), respectively. The outstanding photocatalytic performance for hydrogen production originates from the remarkably improved visible light harvesting capability, the notably promoted separation and recombination inhibition of photoinduced charge carriers, and the increased amount of active sites and the strengthened mass transfer resulting from the combination effect of the porous feature, as-formed defects, and the enlarged specific surface area. Moreover, this approach could render a new insight for designing highly efficient visible light photocatalysts for the other transformations including CO2 reduction, environmental remediation, and organic synthesis process.