The compound parabolic collector (CPC) is a widely used technology in photochemical applications, like photocatalytic reactions. For kinetic purposes in this kind of reaction, the radiation distribution has to be well known, since the reaction rate is strongly dependent on the photon absorption rate. The present work develops a mathematical model which allows simulating the reflection of direct solar radiation on a CPC. Using analytical geometry and vector calculation, equations were evaluated, first for calculating the Cartesian coordinates of the reflecting surface. Later these points are used to calculate incident and reflected rays layouts on the collector. Visual Basic (Excel environment) program was developed for data generation and plotting the reflected rays at any instant. The incident radiation on the receptor was plotted separately displaying the daily direct energy distribution in the absorber. Also the involute length (collector) was calculated with these data, which can be very useful information for collector construction. Results obtained after simulations show that the distribution of incident energy on the absorber surface depends on the surface reflectivity. The incident energy is larger at the top of the absorber than the bottom zone and it is more convenient higher surface reflectivities for more uniform energy distributions. This mathematical model can be a first approach for absorption models which include direct solar radiation in photochemical or photothermal applications.