Abstract: Based on the mechanical aspect of formation of hot cracks in weldments, a new method, accomplished by Synchronous Rolling During Welding (SRDW) along both sides of the weld at a suitable distance behind the welding arc, and its theory have been developed for preventing weld from hot cracking. With the specially developed HNJ— 1 type welding and synchronous rolling machine, experiments were performed to investigate the effectiveness and feasibility of this method. Both theoretical calculation and experiment results show that weld hot cracking in LY12CZ aluminium alloy can be very effectively prevented by the new method. It is an important new solution for prevention of weld hot cracking in welding of sheet metals.