Owing to the high structural designability and functional tunability, covalent organic frameworks (COFs) have emerged as a promising platform for designing excellent photocatalyst candidates. However, their photocatalytic performances are still hindered by insufficient separation and transfer of photo-generated charge carriers. The ordered alignment of the electron donor (D) and acceptor (A) in two-dimensional COFs can promote charge carrier separation upon photoexcitation and provide a favorable pathway for exciton transport, and thus is advantageous for photocatalysis. In this work, we report a new D–A COF that was constructed from the electron-rich phenothiazine (PTZ) and electron-deficient triazine (TTA) subunits, giving rise to a segregated bicontinuous D–A heterostructure within the framework. In comparison to the triphenylamine (TPA) based analogue COF with smaller D–A contrast, this newly designed PTZ–TTA-COF exhibited lower exciton binding energy and enhanced charge separation/transfer. As a consequence, it revealed remarkably enhanced photocatalytic ability in oxidative amine coupling and cyclization of thioamide to 1,2,4-thiadiazole reactions under visible light and in air. This study will provide a rational guidance for developing high-performance polymeric photocatalysts based on D–A structural COFs through the molecular-level design strategy.