Abstract: Effect of induction hardening heat treatment on mechanical properties of 10CrNi3MoV symmetric bulb flat steel was studied in this paper. The results showed the quenching temperature of bulb flat steel was lowered with the increase of roller frequency. Provided the roller frequency in a range of 7~11 Hz,the reheating temperature could be govened to reach 840~890 ℃. The induction hardening temperature and quenching water also affect mechanical properties of symmetric bulb flat steel. The yield strength of flat significantly decreased with the rise of quenching temperature and decrease of quenching water. Second quench and tempered heat treatment would bring about great decrease of the yield strength of bulb flat steel and rising the austenization temperature and improving austenite homogeneity are of benefit to the yield strength. Short stay in high temperature and poor austenite homogeneity help to get thinner martensite and bainite compound microstructures,so that the yield strength of induction hardening and tempered bulb flat steel greatly improved compared with furnace heating treatment.