A new analysis method is proposed for calculating the flux density distribution on focal plane of solar concentrators. On the basis of considering the optical errors and the influence factors which are the sunshape,the random surface error of concentrators, the tracking error, the position error of receivers, the diffuse reflection and the shadow of receivers, with the optical properties of concentrators, the finite element method is used to calculate the flux distribution on the focal plane. The validity and the feasibility of the method are demonstrated by comparing results with those in references. The flux density of hemispheric receiver and cylindrical receiver are also calculated. The results show that the method is independent of the surface contour of concentrators or receivers. It is a simple and universal method that establishes the base for optimizing the system efficiency and measuring the flux-density distribution.