Abstract: In the shipbuilding process, SAW (submerged arc welding) is the main welding process for long plate butt joining. while the use of solo structure laser sensor will bring prepositive errors caused by rail installation. For these reasons, a new SAW seam tracking system was developed based on dual structure laser sensor. The mathematical model of dual structure laser sensor was established on the basis of structured-light imaging principle. According to the mathematical model, the position and offset of welds were obtained. In connection with the characteristics of SAW, the dual structure laser sensor and image processing algorithm of V-groove weld were developed, and experiments were performed to testify the sensor and seam tracking system. The results show that the sensor can be used to detect the position and shape of welds and the system can meet the need of practical welding perfectly.