The importance of study on fracture surfaces,fractal theory and measurements of fractal dimensions are introduced.Based on the fractional dimension testing instrument of concrete fracture surface designed by myself, the fracture surfaces were tested.Using fractals,the fracture surfaces obtained by experiments was analyzed and the information such as fractal dimensions was obtained.The relations between fractal dimensions of the fracture surfaces and interfacial bond strength of old-new concrete were discussed.The experimental results and theoretical ana-(lysis) show that the predicted value of interfacial bond strength of old-new concrete is more precise when the roughness of old concrete fracture surface is characterized with fractional dimension D.When new concrete with higher strength grade is cast,the higher the roughness of old concrete fracture surface(bigger fractional dimension D) is,the higher the interfacial bond strength of old(-new) concrete is.