The highlighted light band with a dark stripe under the collector tubes is the main optical characteristic of parabolic trough solar collectors. Based on research on the formation mechanism of light band, it is derived theoretically that the arc length of light band is related to three parameters, viz. the opening width and the focal length of parabolic trough concentrator and the diameter of collector tube. In addition, the influence of the three parameters on the arc length is different from each other. At the same time, the arc length of the dark stripe in the light band is related to the three parameters as well. After optimization, it is considered that the ratio of the focal length of paraboloid and the diameter of collector tube should be far away from 12.5.