Abstract: The thermal process for a circular thin-walled part in gas metal arc (GMA) based additive manufacturing is researched via numerical simulation, and the validity of the model is tested based on the thermal cycle experiment. Then, the effect of substrate thickness on the temperature field of deposition process is investigated. The results show that the maximum temperature in the molten pool decreases with the increase of the substrate thickness. The length of molten pool enlarges, and the trailing conditions improved significantly. With the increase of the substrate thickness, the peaks and trough values of the first thermal cycling curve decline gradually. The difference of peak temperature increases first, then keeps steady, whereas the difference of tough values stays stable first then decreases. The axial maximum temperature gradient near molten pool increases along with the increment of substrate thickness, but the increasing amount of temperature gradient declines. At the ending moment of deposition, the axial gradient of each middle point in deposition layers increases as the substrate thickness increases. However, with the increase of the deposition height, increasing tendency becomes weak.