The effect of polypropylene fibres(PP fibres) on fracture properties of ultra high strength concrete(UHSC)， which has compressive strength of more than 100MPa， were studied by the method of three point bending beam test. The results show that the development of crack in UHSC can be defined in three stages， and PP fibres are more effective to prevent the development of crack in third stage than in first and second stages. Compared to the UHSC without PP fibres added， the fracture energy and toughness of UHSC with 2kg·m-3 PP fibres of length of 19mm added are increased by 508% and 545% respectively， the compressive strengths at different ages are also increased, and the fracture energy and toughness of UHSC with 2kg·m-3 PP fibres of length of 9mm added are increased by 455% and 294% respectively， but the compressive strengths at different ages are decreased.