Heterocyclic organic semiconductors have attracted significant attention as photocatalysts for hydrogen evolution due to excellent absorbency and abundant active sites. Herein, we developed a dual heterocyclic (O/S) conjugated microporous polymer Py-Th-Fu, consisting of both the furan and thiophene heterocycles, for photocatalytic H2 evolution. Compared with the furan O-heterocycle Py-Fu and thiophene S-heterocycle Py-Th, the Py-Th-Fu with the dual heterocyclic structure is more outstanding in regulating the optoelectronic properties, morphological properties, electric charge shift kinetics, and photocatalytic H2 evolution activity. Computational analysis also elucidates the smallest hydrogen adsorption free energy of Py-Th-Fu, which suggests it is the most advantageous for hydrogen mass transfer in this dual heterocycle polymer. As a result, the synergistic combination of two different heteroatom catalytic sites enables the dual heterocycle Py-Th-Fu to afford enhanced catalytic activity with an optimal rate of 23.28 mmol g−1 h−1, which is nearly equal to 5.06 and 1.58 times that of the corresponding O- and S-containing single heterocycles Py-Fu and Py-Th under visible lighting (λ > 420 nm). Our study demonstrates that the dual heterocyclic strategy using ternary copolymerization to tune the optoelectronic properties may open the horizon for fabricating high-performance photocatalytic water splitting via sunlight-driven hydrogen evolution.