The purpose of this experiment is to find the effects on structures and cementite of rapid induced heating and tempering. The author designed a travelling magnetic field device, using a frequency conversion power supplier, the well prepared SS400 plates were heated, and some parameters are investigated through changing their values (frequency, current, gap from the pole surface to the steel plate and heating time). The temperatures during the heating process are recorded continuously. Meanwhile, the structures and hardness are investigated. The results show that the heating temperature affected the structure and the low temperature impact energy of the steel, at a suitable process parameters combining, the size and morphology of the separation and precipitation particles are very fine and distributed uniformity inside grains.