Abstract: In order to achieve the fast and accurate detection of weld defects in oil and gas pipeline, the weld defect detection method using pulsed laser excitation ultrasonic and dual-wave mixing interferometer ultrasonic detection technologies are proposed. Through studying the mechanisms of both ultrasonic detection technologies, the scheme of simultaneous detection of weld defects and wall thickness of the pipeline is put forward. Moreover, the ultrasonic testing equipment with compact and reliable structure and easy operation is developed; the indicators of the prototype are tested. Using the nanosecond pulse laser as the ultrasonic irradiation source, ultrasonic irradiation and testing experiment are conducted on pipeline weld specimen with different thicknesses. The results show that this ultrasonic testing equipment can effectively restrain the signal noise caused by low-frequency environmental vibration and has very high detection sensitivity on the ultrasonic signal of rough surface. This detection system can effectively detect the ultrasonic echo-signal of steel pipe bottom and inside weld defects, and the wall thickness and defect depth are determined with the TOFD method.