In this paper, a porous two-dimensional CdSNPs@Zr-BTB composite photocatalyst driven by visible light was successfully synthesized by CO₂ expansion liquid in supercritical system, which can degrade methylene blue rapidly and stably compared with ordinary CdSNPs@Zr-BTB composite photocatalyst. The structure and morphology analysis show that the modified Zr-BTB nanosheet can form an optimal nanosheet with 17.8 nm aperture and 1.6 nm thickness. The XRD and Raman spectra showed that CdS was loaded on the nanosheets. The photocurrent, EIS, UV–vis DRS and PL spectra illustrate that CdSNPs@Zr-BTB(7 MPa) has a strong photoelectric effect. The degradation rate of two-dimensional CdSNPs@Zr-BTB composite photocatalyst can reach 98% under light, and the photocatalytic efficiency remains at 82.15% after 5 photocatalytic cycles. The density functional theory analysis shows that the electron cloud distribution between CdSNPs and Zr-BTB is beneficial to the transformation of organic pollutants under visible light irradiation.