Abstract: Poor penetration phenomena such as severe grass echo and heavy bottom wave loss were found when ultrasonic testing to a batch of rings with the unqualified ratio of 14%.The length of poor penetration area along circumferential direction was about 1/6 of the ring circumference.At the same time,the hardness of the rings was also lower than the specific value.Means such as chemical compositions analysis,metallographic examination were used to analyze the reasons for the poor penetration phenomenon.The results show that ultrasonic testing poor penetration of the rings was caused by the fact that the coarse crystal grain of rolling state was not completely eliminated because of the lower heat treated temperature.