In recent years, the use of polymer fibers has had a significant expansion in concrete reinforcement. The main role of the fiber in the behavior after the cracking of reinforced concrete beams is shown. A careful study of cracking behavior requires the use of the concepts of fracture mechanics in the fracture process and the extension of the cracking of concrete beams. In this study, 14 concrete specimens of 100 × 100 × 400 mm with a hole at a depth of 35 mm were subjected to a four-point bending test. In these samples, composition, geometry and percentage of different fiber combinations were varied. The results showed that macro polypropylene fibers, despite the increase in flexural strength, have no significant effect on the increase of concrete ductility. Micro polyester and polypropylene fibers have a better function during concrete cracking, and there was no significant drop in the load for samples containing these fibers when cracking began. Also, the results of composite samples containing macro polypropylene and micro polyester fibers showed that although increasing the percentage of macro fiber, bending strength increased cracking, but the ductility indexes were reduced by decreasing. The results showed that, taking into account the sum of the characteristics, the sample with the ratio of macro polypropylene fibers to the micro polyester fibers of 3 to 2 has the best performance.