[en] The construction of a Z-scheme photocatalytic system is significant in realizing efficient water splitting for hydrogen (H${}_2$) evolution. Herein, a novel donor-acceptor covalent organic polymer (COP) is introduced to construct a COP-ZnIn${}_2$S${}_4$ (ZIS) heterostructure via in situ condensation reaction. The COP-ZIS heterostructure with platinum (Pt) as cocatalyst delivers a high hydrogen evolution rate of 5.04 mmol g${}^{-<!--\; ???\; -->1}$ h${}^{-<!--\; ???\; -->1}$, which is 16 and 3 times higher than ZIS and Pt/ZIS, respectively. The built-in field between the highest occupied molecular orbital of COP and the valence band (VB) of ZIS forms a Z-scheme heterostructure, realizing efficient charge separation. Based on density functional theory calculations, the porphyrin molecule in COP act as electron donor that provides compensating electrons to ZIS. The cocatalyst boosts the utilization of electrons in ZIS. The rate-limiting steps for H${}_2$ evolution with ZIS are overcome by improving charge separation with the Z-scheme heterostructure and speeding up the reaction with cocatalyst. Therefore, the COP-ZIS heterostructure with Pt exhibits optimized H${}_2$ evolution. This study will inspire to construct novel organic and inorganic Z-scheme photocatalysts for efficient green energy production. (© 2022 Wiley‐VCH GmbH)