An important concern in forming is whether the desired deformation can be accomplished without cracking or fracture of the work material. In this research, based on the cracking specimens obtained from hot compression experiment, the fracture behavior of as-cast highly β stabilized Ti40 alloy was investigated at the deformation temperatures of 1123-1373K, strain rates of 0.01-10s-1 and height reduction of 70%. The main fracture modes consisted of 45o shear fracture and longitudinal cracking occurred on free-surface, as well as inner cracking occurred at the triple boundary junctions. Moreover, the influence of deformation parameters on fracture mechanism was analyzed emphatically in terms of SEM. At low temperature of 1123K the transgranular cleavage brittle fracture was observed, at 1273K the ductile fracture occurs, at high temperature of 1373K a large number of small dimples on the fracture interface are examined. Furthermore, the effect of strain rate on the fracture behavior of as-cast Ti40 alloy is significant. At 0.01s-1, the fracture did not occur. At the strain rates of 0.1 and 1s-1, the fracture surface is covered with a large amount of dimples indicating that the fracture mode is ductile fracture, while at high strain rate of 10s-1, the fracture surface appears brittle fracture feature. Finally, the damage mechanism and fracture reason were discussed and fracture principle diagram was drawn for the as-cast Ti40 titanium alloy.