Abstract: The weldability of A517Q rack steel was investigated systematically by means of oblique Y-groove cracking tests, maximum hardness tests on the heat affected zone (HAZ) and the mechanical property tests of welded joint. The results showed that under the restraint condition, the cold crack susceptibility of A517Q weld was increased with the thickness of tested plates increasing from 30 mm to 60 mm. Raising preheating temperature contributed to the reduction of cold crack tendency of steel and the hard level of HAZ. The welded joint of 177.8 mm thick A517Q rack steel plate exhibited high strength and toughness, meeting the requirements of usage. The microstructure of HAZ mainly consisted of lath-like martensite and lath-like bainite. The hardness of HAZ apparently exceeded weld metal zone and the parent metal, presenting a high harden tendency and a certain risk of cold cracking.