Based on the comparison test platform of the dual-axis tracking trough solar system, the effect of the dust accumulation on the photothermal performance of the trough solar energy system is studied through theoretical analysis and experimental tests. The dust reflection factor and correction coefficient of the acquisition factor are introduced to quantify the effect of dust accumulation on the photothermal performance of the system. The results show that the dust on the condenser has a significant effect on the concentrating characteristic of the focal plane. The uneven distribution of the dust causes more serious scattered radiation. As the amount of dust increases, the energy obtained by the focal plane within a certain size decreases. The energy flux density at the center of the focal plane is reduced, and the receiver with small aperture is more sensitive to the change of energy that can be collected on the focal plane. To ensure the correction coefficient of the acquisition factor of the trough concentrator is greater than 0.90, the dust reflection factor should be less than 4.3%. A prediction model of the effect of dust accumulation on the heat collection performance of the trough solar system is established and verified by the experimental test. The relative error between the predicted value of the model and the experimental value is less than 5.07%, and the good agreement between them is obtained. This prediction method has good universality and can provide theoretical guidance for practical engineering applications.