Covalent triazine framework (CTF)-based photocatalytic materials are excellent structural platforms due to their good photocatalytic performance and scalability, but their high recombination probability of photogenerated carriers remains a difficulty to solve. Therefore, we synthesized a partially nonplanar Tppo-CTF through a bottom-up strategy that introduces nonplanar triphenylphosphine oxide (Tppo) into the planar structure of the CTF. Specifically, the unique nonplanar structure of Tppo weakens the interlayer force and enables the synthesis of the few-layer Tppo-CTF. Meanwhile, the strong electron withdrawing effect of Tppo fragments in the Tppo-CTF can effectively promote the separation and inhibit the recombination of photogenerated carriers. In deionized water containing triethanolamine (TEOA) as the electron donor, the HER rate of the 4-Tppo-CTF reaches 15.685 mmol h−1 g−1, which is 4.6 times higher than that of the bulk CTF. Remarkably, when deionized water is replaced with seawater, the 4-Tppo-CTF still achieves a high HER rate of 12.799 mmol h−1 g−1. This strategy provides a reference for the design and construction of high-efficiency CTF-based photocatalytic materials.