Abstract: Beryllium and Al-Mg alloy was welded by Nd:YAG laser. The reasonable welding parameter was obtained. The microstructure of beryllium and Al-Mg welding seam was analysed by means of X-ray energy spectrum, scanning electron microscope and electron probe microanalysis. The microstructure of welding seam is affected by cooling rates. The microstructure of welds consists of dendritic structure near melted line and equiaxed grain at the centerline of welding seam. Hot cracking and inclusion are main defects. These inclusions are formed by C, O, Al, Mg, F and Cl elements. The results of surface scanning show that C and O elements segregation exist surface layer of welding seam, on the other hand distribution of Mg and Be is uniformity.