Abstract: Andlysis on the crack produced in automatic submerged arc welding test of the high-toughness refractory and weather-resistance construction steel WGJ510C2 newly developed in Wuhan Steel was taken by means of optical microscope,electron probe,and transmission electron microscope.It shows that crack in weld started in outside welding zone and expanded to the continuous tack welding zone is crystallization-crack.The dendritic structure existing crack is coarsen revered to the normal side.More network proeutectoid ferrite is in the crack side,but little in the normal side.The fracture surface is intercrystalline failure,both of the outside welding zone and the joint part of outside welding and continuous tack welding existed the second intercrystalline crack.Coarse columnar structure zone in outside welding has obvious high temperature oxidation in the face,and equiaxed grain zone in the continuous tack welding has little oxidation.The cracks produced in the automatic SAW welding test are existed in the weld,and has nothing obviously with WGJ510C2 steel.