Laser welding technology and defect of sandwich diamond saw are systemically researched with RofinDC025 laser. The result indicates that a mass of porosities and more Cu are the main welded defect in the welding. The porosities produced by the action together of impurities in the interlayer and powder metallurgy material can be reduced mostly when welding depth is body′s 1/2 in one side and body′s 100% in another side or improving the welding speed. The Cu that produced by the melting Cu plate in the body can be reduced when the lasering lean to the diamond segment. The right welding parameters of 350 mm sandwich saw are that the laser offset is 0～+0.20 mm, in one side the welding line energy is 25～40 J/mm with the laser power under 1000 W, in another side the welding line energy is 80～150 J/mm with the laser power excess 1500 W. Under this optimization condition, the content of Cu is about 0.2%～1.1% in the welded zone, the porosities are less, and the welded blend intensity is up to EN13236 safety standard.