Abstract: The cause of the local incomplete brazing at the root of the bond line of the fushion-brazed joint between aluminium and steel was studied, and the relevant measures were developed to restrain or avoid the defect.Analysis results showed that insufficient heat input is the essential cause to form the cocal incomplete brazing defect, and the temperature of the molten pool and the steel sheet at the the root of the bond line can not reach the critical brazing temperature to achieve a brazing joint using Al-Si brazing filler metal which is the direct reason of cocal incomplete srazing.Moreover the local incomplete brazing is indirectly influenced by the fluid flow of the molten pool and the heat dissipation of base metals.The local incomplete brazing defect can be restrained or avoided by increasing the heat input or adjusting the location of the laser spot and arc.