This work investigates the influence of the concentrated illumination characteristics on the electrical output performance of photovoltaic/thermal system under trough concentrated sunlight. By measuring the illumination distribution at the focal plane for different distances and different opening widths of mirror with the CCD camera, the illumination value distribution matrix is acquired, from which illumination parameters such as average illumination value, nonuniformity, peak deviation degree and illumination utilization ratio are extracted. The double exponential equivalent circuit model of the concentrator solar cell array is acquired by introducing recombination mechanism and parasitic resistance of the cell under the concentrated sunlight, and the simulation results agree well with the experimental records. The results show that the short circuit current and the relative maximum power increase with the increase of the relative average illumination value, and the degree of increase becomes smaller due to the intensifying of the recombination mechanisms and the increase of the ohmic losses for parasitic resistance, respectively. The open circuit voltage decreases with the increase of the non-uniform illumination degree and the peak deviation degree. The relative average illumination value has a greatest influence on the fill factor because of the ohmic losses for parasitic resistance. The conversion efficiency of solar cell depends on the illumination utilization ratio and the relative average illumination value. Taking series array of 6 pieces of 2 cm×2 cm back contact cells as an example, it can be concluded that, when the opening width of mirror is 157 cm and the distance from focal plane is 2 cm, the illumination distribution is the most suitable for the performance output of the back contact solar cell array.