Covalent organic frameworks (COFs) with crystalline networks and large surface areas provide an ideal platform to mimic natural structures for photosynthesis. However, it remains challenging to construct complex, multistate architectures using single-component COFs. Herein, inspired by leaf morphology, we demonstrate a one-pot synthesis for constructing a one-dimensional (1D) COF and a three-dimensional (3D) COF from identical binary monomers, yielding a hierarchically integrated COF heterostructure (1D@3DCOF-2). The 1D chains and 3D porous frameworks form in situ and are spatially integrated, forming a homogeneous S-scheme heterojunction that yields a built-in electric field for enhanced charge carrier dynamics. The hydrophilic 1D COF possesses excellent light-harvesting and Pt anchoring capacities, and the porous 3D COF ensures efficient mass transfer. With Pt as a cocatalyst, 1D@3DCOF-2 achieved an excellent hydrogen evolution rate (HER) of 45.7 mmol g⁻¹ h⁻¹ under visible light irradiation, surpassing that of the individual 3D COF (31.1 mmol g⁻¹ h⁻¹) and inactive 1D COF. Additionally, a higher rate up to 50.8 mmol g⁻¹ h⁻¹ was achieved in seawater. This work establishes a one-pot synthetic strategy for constructing multistage COFs towards nature-inspired high-performance heterostructures. (Figure presented.)