Abstract: A mobile robot for welding of ship deck is developed with the function of auto-searching weld line.The wheeled motion mechanism is used for the welding robot.In addition,a cross adjustment slider is mounted on the body of robot,and the system can obtain two dimension deviation signals by scanning the weld groove with laser-PSD style displacement sensor.A digital signal processor is used as CPU of the system.Moreover several special motion controllers and drivers are used for servosystem so as to make multi-freedom work in spase coordinately.Within deviation range,the system makes the robot body track seam roughly,while making the cross slider track seam accurately in real time.Furthermore,the system has the function of auto-searching track,namely,auto-searching weld line according to the characteristics of weld groove and adjusting its posture to the desired status for welding.The experiment of auto-searching track shows that the robot has high tracing accuracy,and can meet the requirement of practical welding.