Portland cement, crushed stone, sand and superplasticizer were used to obtain a high strength concrete with a low water to binder ratio. A reticular polypropylene fiber and a single polypropylene fiber were used to improve the strength of the high strength concrete, but the effects of the two fibers on the slump and strengths were quite different. The reasons of the differences were the surface area and the modulus of elasticity of the fibers. The results show the reticular fiber was better to used in high strength concretes.