A new method is proposed for calculating the energy-flux-density distribution on focal plane of trough solar concentrators. According to the geometric optical properties of parabolic trough concentrator (PTC), the calculation formulae for incident point coordinate (along the width direction) of incident ray on the focal plane is derived. The sun′s disk model (Buie model) is developed to a linear model of axis symmetry. The energy flux density distribution on linear focal plane is characterized by using frequency statistics function of Origin software, and finally the test is performed with a CCD camera. This calculation method is simple and clear in the function relation, which requires no programming and less calculation, and is applicable for arbitrary surface contour of concentrators and linear receivers. It can offer useful reference for design and optimization of the trough solar concentrating systems.