The Linear Fresnel Reflector (LFR) is a promising solar concentrating technology because of its simple design and its low cost compared with others concentrating solar technologies. There are different geometrical parameters that can affect the performance of the LFR specially in the trapezoidal secondary reflector. In this work, a comparison between four different geometries of the secondary reflector of an LFR by means of Computational Fluid Dynamics (Ansys Fluent®) is carried out. It is taking into account the variation of the tilt angle of 45°, 50°, 60° and 70° in the trapezoidal geometry with a constant aperture and a constant height. The comparison is made in terms of the absorbed radiation flux in the absorber tube and the entropy generation rate in a global and local way considering an LFR with 25 mirrors. The entropy generation rate considers the phenomena of viscous dissipation, heat transfer and radiation by means of a user-defined function. The trapezoidal geometry of 60° presents an absorbed radiation flux value of 4085.9 W/m2 with a total entropy generation rate of 0.043 W/K with a thermal efficiency value of 0.284. The results of this CFD model can be applied to obtain a better performance of LFRs.