Abstract: By means of macroscopic inspection, chemical composition analysis, mechanical property testing, metallographic examination and so on, the cracking resason of bottom tube of heating furnace for steel rolling was analyzed. The results showed that the cracking reason was due to widmanstatten structure and coarse grain produced by inappropricate heat treatment for raw materials, the toughness and elongation of steel were reduced, under the effect of stress, the cracking occurred in the steel tube at last.