It is difficult to collect the crack propagation signal under general continuous welding condition due to other signal interference of molten pool. In order to study the effect of residual stress on crack propagation, acoustic emission technology was successfully applied to monitor welding process according to the characteristics of pulsed laser welding. Crack free welding is achieved by reducing the pulse interval to limited the crack size of single pulse welding spot. The welding process was monitored synchronously by high speed photography and acoustic emission, the evidence of crack propagation after solidification of weld is successfully captured.