The invention discloses a method for self-trailing of a mobile welding robot before welding, comprising the following steps: a mobile welding robot moves ahead at the angle smaller than or equal to 180 degrees and searches a weld joint from the feature model of a welding groove; the gesture of the mobile welding robot body and the distortion characteristics on the welding groove are combined to obtain the initial digging angle of the mobile welding robot; when the initial digging angle is smaller, precise pose regulation based on the least square method is directly carried out; when the initial digging angle is bigger, position timing or through position timing is selectively carried out; then, precise pose regulation based on the least square method is carried out until the mobile welding robot body is parallel to the welding joint, and a welding gun is positioned on the welding joint center. The invention causes the welding gun and the welding joint to form closed loop and feedback relationship, and the welding gun returns to the welding joint center after adjustment each time; the digging angle obtained on the basis of the least square method is more accurate; thus the invention realizes self-trailing posture adjustment of the mobile welding robot before welding at any angle and welding direction when the digging angle is 0-180 degrees.