Abstract: In order to study influence of welding parameters on root humps in high power fiber laser welding, effect of laser power, welding speed, defocus, flow rate of bottom shielding gas and welding position on root humps was studied based on a single variable method. The results show that, with the increase of laser power, root humps tend to increase at first and then decrease. When welding speed increases, root hump height increases at first and then decreases, root hump spacing decreases significantly. When defocus is near 0mm, root hump tendency is obvious. Under the appropriate flow rate of bottom shielding gas, root hump tendency is reduced. The optimal rate is 15L/min. When welding orientation is 60, root hump tendency decreases to a certain extent. The results show that reasonable welding parameters can eliminate root hump efficiently.