Abstract: The change of environment temperature often affects defect location and ration of ultrasonic testing. Combining with ocean engineering practice, an invariable temperature experiment chest which simulates engineering field environment temperature is designed to investigate the temperature effect on defect location and ration of ultrasonic testing in the range of -20~100 ℃. The relational expression for the change of transversal wave velocity on depth measurement was acquired and used to modify defect location in different temperature. This research performs direction function for ultrasonic testing.