Abstract: The Riccati-Bessel function ratio calculation method is introduced into the Mie scattering theory, and the optical properties of Cu/SiO₂ nanofluid are simulated by combining with the Monte Carlo method, and the influencing factors and applications in photovoltaic/photothermal systems are analyzed. The results show that: the constructed model shows high accuracy in describing the optical properties of the nanofluid, and the errors between the simulation results and the experimental data are within 3.66%; the increase of the nanoparticle concentration, particle size, and the optical length of the fluid increase the spectral absorption ability of the nanofluid, but the influence intervals of these factors are mostly located in the short-wavelength band and the near-infrared region; when the mass ratio of Cu/SiO₂ is 0.001%/0.03% and the optical length is 15 mm, the average transmittance of the nanofluid in the intervals of 300 nm-400 nm, 400 nm-1100 nm, and 1100 nm-1400 nm reaches 67.07%, 77.12%, and 16.39%, respectively, and the optical properties are more suitable for the requirements of frequency-dividing applications.