Abstract: The low temperature fracture toughness of welding metal is different for offshore platform steel when welded in horizontal and vertical positions. Several tests indicate that the toughness values of vertical welding position specimens with high heat input were higher than those of horizontal welding position specimens with low heat input, which are the reverse results of general consensus. Two groups of tests welded by FCAW were conducted, one is in horizontal position and the other one is in vertical position. After the CTOD (Crack Tip Opening Displacement) values were obtained, the macrographs, fracture surface morphologyand microstructure were analyzed. The result showed that the toughness values of vertical welding position specimens were higher than those of horizontal welding position specimens because of columnar crystal structure and slag inclusion.