With numerical modeling in meso level, impaction of incorporating polypropylene fibers with two different geometry dimensions on flexural strength and toughness of hybrid fiber concrete has been studied in this paper. Mechanism of such hybrid fiber reinforcement has also been analyzed. The results show that hybrid of fibers with different geometric dimensions would bring about synergy, thus fiber enhancement effect could be demonstrated. Furthermore, the closer the incorporation ratio of these two kinds fibers are to each other, the more evident the enhancement will be produced. The most optimized hybrid ratio is in between 2:1 and 1:1.