Ultrasonic flaw detector itself has the characteristics of high detection accuracy, fast detection speed, small size, light weight, and its own ultrasonic non-destructive testing, so it has been widely used in many fields. The measurement accuracy of ultrasonic flaw detector has a non-negligible impact on its function, and it will be affected by various factors in the use process, leading to the deviation of the measurement results. Therefore, it is necessary to do a good job of the measurement verification of ultrasonic flaw detector regularly. The metrological verification of ultrasonic flaw detector is studied and discussed from the Angle of ensuring the performance and measurement accuracy of ultrasonic flaw detector and giving full play to the function of the instrument. In the study, the metrological verification process and precautions of ultrasonic flaw detector are defined, and its dynamic range, horizontal linearity, vertical linearity, sensitivity, false positive rate and resolution are verified. The measurement accuracy of ultrasonic flaw detector has been significantly improved before and after comparative verification, and its own performance can be fully brought into play.