Abstract: Effects of adding steel fibers and polypropylene fibers into C50 high performance concrete and different fiber contents on frost resistance of concrete were investigated by fast frost test. The microstructures of fibermatrix interface zones were observed by using scanning electron microscopy, so that the results of macrofrost tests were analyzed from the microstructure point of view. Results showed that by adding polypropylene fibers, the improving effects on frost resistance of concrete was better than by adding steel fibers, although the latter was of better microstructures of fibermatrix interface zone. When adding polypropylene fibers into concrete, there were double effects including, which was crack resistance effect and weak interface zone effects, so that the optimum fiber volume content existed. Adding 1.0 % polypropylene fibers into concrete could achieve the best improving effect of frost resistance, and the relative dynamic elastic modulus was high to 9801 % after 300 times of freezethaw cycles.