The leakage accident of T2 internally ribbed tube in the middle part of spiral water wall in a 660 MW supercritical units was is analyzed by means of macro examination, chemical composition analysis, mechanical property tests, metallographic examination and scanning electron microscope. The results show that the leakage of T2 internally ribbed tube is due to the linear crack caused by improper hot rolling process of tube billet and the manufacturing defects of tube billet. So it should strengthen the surface quality inspection of hot rolled tube billet in manufactory; the inspection for the same batch of T2 internally ribbed tubes should be cairried out timely to eliminate similar defects in power plant.