Abstract: Biochar loaded Ag-doped ZnO composites (Ag-ZnO/Biochar) were prepared with a procedure of sol-gel method and carbonization using zinc acetate (Zn(CH₃COO)₂·2H₂O) as a zinc source, silver nitrate (AgNO₃) as doping source, and cellulose nanocrystal (CNC) as a morphological-inducing template, respectively. The obtained Ag-ZnO/Biochar composites were characterized by TEM, XRD, BET and UV-Vis DRS. The photocatalysis performance of Ag-ZnO/Biochar composites was investigated through the degradation of methylene blue (MB) under visible-light irradiation, and the photocatalysis mechanism of Ag-ZnO/Biochar composites was further studied. The results show that nano ZnO retains a good dispersion after carbonization, and Ag spherical nanoparticles are uniformly dispersed on the surface of ZnO to form Ag-ZnO/Biochar ternary composite. Compared with Ag-ZnO and ZnO/Biochar composites, the photocatalysis property of Ag-ZnO/Biochar composites in the visible-light region is significantly improved, which is attributed to the adsorption ability from biochar and the surface plasmon resonance (SPR) effect from Ag nanoparticles. In particular, the Ag-ZnO/Biochar composites has the best light absorption performance and an optimum degradation efficiency to MB at the mass ratio of 0.01:0.25:1 (AgNO₃:CNC:Zn(CH₃COO)₂·2H₂O), corresponding to 99% degradation rate of MB after the absorption for 30 min in dark condition and continuous irradiation for 120 min under 500 W visible-light at room temperature, which is significantly higher than Ag-ZnO (about 23%) and ZnO/Biochar composites (about 64%).