Numerical prediction of three-dimensional dynamic fracture is very important for the integrity of complicated machine components and vital structures, including manufacturing tools. For the purpose of the present subject, it is important to understand the responses of time varying fracture parameter such as the dynamic J integral or the dynamic stress intensity factor along the curved-crack front in 3-D bodies. However, the mechanism of three-dimensional dynamic fracture has not been clarified. To elucidate it, the authors carried out experimental and computational studies. First, in the experimental study, high-speed photographs of dynamically propagating crack fronts were recorded. In the computational studies, in order to ease the three-dimensional numerical evaluation of the dynamic J integral, an expression in terms of equivalent domain integral (EDI) is used. Furthermore, to overcome the difficulties in three-dimensional dynamic fracture simulation, a three-dimensional moving finite element method together with an automatic element control method is developed. The moving finite element simulation together with the dynamic J integral evaluation procedure makes it possible to calculate accurate distribution of the dynamic energy release rate along the propagating crack-front at each time step. Using the experimentally recorded history of three-dimensional dynamic fracture, the generation-phase simulation is carried out. Based on the dynamic J integral distribution along the dynamically propagating crack fronts, the mechanism of three-dimensional dynamic fracture is discussed.