Nickle base single crystal superalloys DD407 were welded by electron beam welding. the morphology and distribution of crack were analyzed by optical microscopy and scanning electron microscopy. the chemical component between dendrite dry and interdendritic area was measured by EDS. the segregation ration of elements was calculated and the causes of crack formation was analyzed. The results show that: longitudinal cracks, transverse cracks, crater cracks, intergranular cracks mainly were produced in fused region of DD407 under the thermal effect of the electron beam. With the increasing of electron beam current, the content of solidification cracks increase firstly and then decrease when other parameters remain unchanged. low melting point eutectics gather and form a low-melting liquid films due to the serious segregation of alloying elements in miscellaneous grain zone,thus the solidification cracks are often formed in miscellaneous grain zone in the solidification shrinkage tensile stress.