Abstract: Some invalid fracture specimens of Ti-alloy in conditioned fatigue limit test are analyzed. The results show that much higher grip supply pressure is unsuitable for metallic materials with bigger fatigue notch sensitive coefficient.In order to lessen or eliminate the influence of grip supply pressure on fatigue property of round-section specimens, the cross-section area ratio of D²/d² must be increased.The Ti alloy specimens will fracture validly when the ratio of D²/d² isn't less than 3.5