Abstract: By simulation of welding heat cycles,tensile deformation on specimens at constant strain speed under different series of high temperature was studied.Testing results showed that 1350-1450℃ is the sensitive temperature interval of brittle fracture caused by intergranular liquation,and 900-1000℃ is the sensitive temperature interval of low ductility fracture caused by inhomogeneous recrystallization.Under constant strain and high temperature,cracking initiates in the earlier straining stage at the boundaries between the matrix and inclusions or at the liquated grain boundaries,but in the final straining stage,a lot of crackings initiates at the intergranular boundaries of the recrystallized grains.A newcracking model which could be used to interpret the micro-process of the low ductility-tip cracking at high temperature was proposed.