Abstract: Brand 30MnCr22 177.80 mm×10.36 mm steel tube blank was converted to P110 steel tube billet after upgrading by heat treatment. Some cracks were observed on the surface of tube billet in the subsequent nondestructive testing. The crack was sampled for macrofracture analysis, metallographic analysis, fracture scanning analysis and energy spectrum analysis. The property of cracks was determined. It was found that the raw materials of tube billet contained Ti, O, Si and Al. The smelting of steel billet was not pure enough. The stress in the quenching process of heat treatment was too large to induce the formation of quenching cracks. In the process of subsequent production, the formation of such crack defects could be avoided by optimizing the steel billet smelting, selection of quenching temperature in heat treatment as well as control of cooling temperature for steel tube. Therefore, the aims to optimize process and eliminate defect could be achieved.