Graphdiyne (GDY) with a direct bandgap, high charge carrier mobility, and ordered pore structure, is considered an excellent matrix for the construction of heterojunction photocatalysts. However, the traditional fabrication methods for GDY-based heterojunctions require a complicated deprotection of hexakis-[(trimethylsilyl)ethynyl]benzene (HEB-TMS) and usually result in localized heterojunctions. Herein, we developed a facile deprotection-free method to in situ grow GDY on the surface of C3N4 by directly using HEB-TMS as the precursor. Such a method enabled the formation of an integral GDY@C3N4 heterojunction, resulting in a significantly enhanced photocatalytic activity in the visible region. The optimized GDY@C3N4 showed 15.6-fold hydrogen production efficiency compared to pristine C3N4, and outperformed the GDY/C3N4 samples synthesized by other approaches (e.g. physical mixing, hydrothermal treatment and calcination treatment). This study provides a universal and efficient strategy for the design of GDY-based heterojunction photocatalysts for solar-to-hydrogen energy conversion.