Aiming at all position automatic welding of pipeline by robot,a welding deviation measurement method of gas metal arc welding(GMAW) based on monocular active and passive vision is proposed. A kind of dimming glass is designed,so that the same welding image contains the information of laser stripe and welding wire tip. Firstly,according to the characteristic that the noise type of welding image is Gaussian distribution,the LoG operator is used to filter the images of arc area and laser stripe area respectively；then,the image processing algorithm is designed to extract the coordinates of welding wire and weld groove center；finally,the deviation value of two coordinate points in Y axis direction is calculated. The experiment shows that this method can measure the welding deviation in real time in the welding image of the filling welding,and the welding error can be controlled within 0.2mm,which can provide a reliable basis for realizing the automatic seam tracking control of the pipeline welding robot.