简要分析了水声距变化引起检测结果异常的原因，结合转台喷水式超声波C扫描检测系统的特点，利用超声检测仪第一界面回波实时测量水声距，并作为反馈值对运动机构进行闭环控制，自动跟随水声距，同时采用样条插值技术实时拟合DAC(距离-波幅)曲线，修正由于机械机构动作延迟和间隙引起的水声距的微小偏移。利用上述方法对存在大于φ1.2 mm当量缺陷的环形锻件进行了检测试验。结果表明：采用水声距自动修正方法的检测结果的信噪比明显优于未进行修正的结果，缺陷清晰可辨，对同类检测系统的研制及应用具有实际参考意义。

The reasons of abnormal test results because of water path length changes were briefly analyzed. Considering the characteristics of the ring forgings ultrasonic C-scan system, the first interface echo time of ultrasonic flaw detector was used to measure the water path length and the value was further used as a feedback of the actuator for closed loop control. To correct the offset due to mechanical system operation delay and backlash, DAC curve was drawn in real time with spline interpolation technique. For one ring forging with larger than φ1.2 mm equivalent defect, experiments were carried out on the above-mentioned method. The results showed that actual picture quality and the accuracy were better than those that were not corrected. And this paper maybe provides engineering reference value.