Pt nanoparticles (PtNPs) as active species have always been considered as one of the best semiconductor materials for photocatalytic hydrogen production. In this study, a Schottky heterojunction has been successfully constructed by evenly loading ultrafine PtNPs onto a triazine-based covalent organic frameworks (COFs). This strategy maintained the high activity of these ultra-small PtNPs while maximizing the utilization of the Pt active sites. The fabricated PtNPs@covalent triazine-based framework-1 (CTF-1) composite accomplished a significantly high rate of hydrogen evolution (20.0 mmol·g−1·h−1, apparent quantum efficiency (AQE) = 7.6%, at λ = 450 nm) with 0.40 wt.% Pt loading, giving rise to a 44-fold-increase in the efficiency of the photocatalytic hydrogen production compared to the pristine CTF-1. Theoretical calculations revealed that the strong electron transfer (Q(Pt) = −0.726 qe, in the analysis of Bader charge, Q(Pt) is the charge quantity transferred from Pt cluster to CTF-1, and qe is the unit of charge transfer quantity) between PtNPs and CTF-1 triggers a strong interaction, which makes PtNPs being firmly attached to the structure of CTF-1, thereby enabling high stability and excellent hydrogen production efficiency. Importantly, the hydrogen binding free energy (ΔGH*) of PtNPs@CTF-1 is much lower than that of the unmodified CTF-1, leading to a much lower intermediate state and hence a significant improvement in photocatalytic performance. The overall findings of this work provide a new platform to incorporate metallic NPs into COFs for the design and fabrication of highly efficient photocatalysts.