The 3 mm thick high-strength steels are taken as test materials and the technique of fiber laser-arc hybrid welding assisted by metal inert gas is chosen. The effects of laser power and arc voltage at welding speed of 5 m·min -1 on weld appearances are investigated. The comparison with those weld appearances generated in low speed welding of thick plates is conducted. The research results show that the increases of laser power and arc voltage can ensure the improvement of welding stability and the obtainment of good weld formation. There exist different shallow and deep Y-type weld appearances at different heat source positions. The high-speed photography indicates that the droplet size is relatively large in the laser leading mode. In addition, it is prone to vaporization and explosion in the transfer process. Thus, the impact on molten pool are relatively strong. In contrast, in the arc leading mode, the keyholes are stable. The liquid metal flows down along the keyhole walls and thus the bottom area of molten pool increases. As for the low speed welding of thick plates, the weld appearances are not consistent with those for high speed welding of thin plates due to the differences in welding line energy and surface tension of workpieces.