Abstract: Laser gas metal arc welding was carried out on 20 mm thick EH36 steel planes to study effects of relative position of thermal source of laser-arc hybrid welding on macroscopic morphology, microstructure, burning rate of alloy and properties of the welded joint. The results show that compared with those of the arc leading welding, for the laser leading welding, the welding seam penetration is shallower, the welding width is bigger, the penetration ratio and the burning rate of alloy are lower, the welded joint becomes less symmetrical and the microhardness of top zone in the welding seam is lower. The grains of welding, large and coarse, are subjected to grow to the surface center of the molten pool by laser leading welding, while the grains of the welding are finer and grow towards the center of the seam by arc leading welding. The reason for such differences is that the position of the heat source is different so that the total energy in welding seam and the direction of molten pool flow are different.