In a "thermally decoupled" PV/T system, photovoltaic and thermal absorbers are allowed to operate at different temperatures to utilize full-spectrum sunlight. In this study, a two-axis tracking PV/T system with a SiO2/TiO2 interference thin film (irradiated by natural sunlight) was designed and fabricated initially. The SiO2/TiO2 interference thin film designed by the authors achieved a high average reflectance (R >= 96.8%) for PV bands, with a high average transmittance (T >= 85%) at 1100-2500 nm. The photoelectric, photothermal, and overall efficiencies were tested and analyzed theoretically using the first and second laws of thermodynamics. Outdoor testing indicated that PV cells with SiO2/TiO2 interference thin film can decrease by 3.0 K, and that the power generation and efficiency of the PV cells can be improved by 10% and 0.65%, respectively. The overall energy and exergy efficiency of the PV/T system based on SiO2/TiO2 interference thin film can reach 22.72% and 18.81%, i.e., 4.94% and 1.03% higher than those without a SiO2/TiO2 interference thin film, respectively. The calculated payback time was 17 years for this PV/T system.