Inhibition of the recombination of photo-induced electrons and holes is critical for light harvesting and enhancing the photocatalytic efficiency of hydrogen production in metal–organic frameworks (MOFs). Herein, Cs₃Bi₂I₉ (CBI) quantum dots (QDs) were firstly loaded into the inner pores of MOF NH₂-UiO-66 (U6N) through an anti-solvent recrystallization (ASR) method. The light adsorption wavelength of the MOF composite was significantly extended to the visible region, and remarkably, the complementary electronic band structures between MOF and CBI resulted in spatial separation of photogenerated electron–hole pairs in this material. Thereby, under visible light irradiation, the prepared catalysts exhibited high H₂ production activity of 32.21 μmol g⁻¹ h⁻¹ that originated from photocatalytic proton reduction without introducing noble metals, far surpassing the MOF and CBI counterparts. In addition, under the synergistic effect of CBI QDs and low-coordination Pt metal clusters, the photocatalytic hydrogen production rate can be further improved to 141.87 μmol g⁻¹ h⁻¹ with a TON value of 17.74. The electron migration mechanism among CBI and U6N, and the microstructure of low coordination Pt clusters was also investigated through transient absorption spectra (TAS) and X-ray absorption spectra (XAS).