The dynamic three-point bending loading was carried out on Ti6321 titanium alloy to cause mode I (open type) fracture and obtain the waveform curve. Combined with the experimental & numerical method, the mode I crack dynamic fracture properties of Ti6321 titanium alloy with three structures were obtained. The fracture surfaces of three kinds of Ti6321 titanium alloys were observed and analyzed by scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM). The results show that the widmanstatten structure has the highest dynamic fracture performance of mode I crack, followed by the bimodal structure, and the equiaxed structure has the lowest dynamic fracture performance. For mode I crack fracture, equiaxed structure and bimodal structure are mainly ductile fracture mechanism, while widmanstatten structure has the characteristics of partial cleavage fracture. The Widmanstatten structure has the best fracture performance. Because of the largest fluctuation of fracture and the largest specific surface area, the crack propagation needs more energy.