Abstract: Taking different pipeline steels as the research object, the differences of lateral expansion values measured by image analysis method, vernier caliper method and lateral expansion meter method were compared, and the accuracy and stability of determining the ductile-brittle transition temperature by side expansion value were verified. The Charpy impact test of X80 steel solid wire automatic welding girth weld at different temperatures was carried out. The results show that for materials with poor toughness and uneven toughness, as well as samples with distortion after impact fracture, the lateral expansion value should be measured by lateral expansion instrument. For pipeline steel, the accuracy and stability of the results of the ductile-brittle transition temperature determined by the side expansion value were good. The lateral expansion value corresponding to the ductile-brittle transition temperature of X80 steel solid wire automatic welding girth weld was 0.90 mm.