Abstract: For the demand of low heat input and high quality welding technology, the difference in multi-pass welding techniques for thick aluminum alloy plates with CMT welding and pulse MIG welding was investigated. The thermal cycles during welding were measured; the microstructure and mechanical properties (tensile, bending and microhardness) of the welded joint were analyzed. The tests show that comparing to pulse MIG welding, CMT welding technology could make weld with lower temperature field, decrease the softened zone, increase the impact toughness of the joint, and improve the weld microstructure significantly. The experimental results show that CMT welding can make better weld on thick aluminum alloy plate.