Abstract: In the light of abnormal fracture of DWTT test for high-grade pipe steel, the paper statistically analyzes the DWTT test results for X65, X70 and X80 pipe steel at a systemic temperature and studies their abnormal fracture rules. The study results show that the probability of abnormal fracture of pipe steels is increased with the pipe thickness, trending towards a high probability with the pipe thickness increases, while the temperature zones of abnormal fracture is closely related with FATT 85.