Abstract: Polypropylene fiber is a new measure to prevent plastic cracks of concrete. Effects of the parameters, such as dosage and types of fibers, on the plastic cracks were studied systematically. The properties of cracking resistance of mortar, ordinary concrete and high performance concrete were investigated using samples of two types in shape. The results show that: (1) Polypropylene fibers may increase the cracking resistance of concrete significantly and increasing the dosage of fibers may increase cracking resistance of concrete further; (2) As smaller quantity of cement and higher quantity of aggregate as possible should be used to prevent concrete from cracking; (3) The main causes why polypropylene fibers increase cracking resistance of concrete are increasing strain capacity of concrete at an early age, decreasing shrinkage strain, improving plastic tensile strength and decreasing tensile stress of the capillary.