Laser and plasma arc are used as two kinds of high energy beam heat sources for composite welding. Compared to laser welding alone, it can achieve greater penetration and higher welding speed. The 304 stainless steel plates with 2 mm and 4 mm thickness are used as the base metal for flat plate welding and butt welding respectively. The weld formation and the plasma shape under different laser powers are observed. Under the premise of ensuring double-sided formation for single-sided welding, the optimal current matching range of different laser powers and the adaptability of 4 mm thick stainless steel in the butt welding for gap and misalignment are studied in the 2 mm flat-plate high-speed welding . The tests show that under the premise of ensuring double-sided formation for single-sided welding and a minimum welding speed of 1 000 mm/min, the larger the laser power is, the wider the current range is matched, and the higher the welding speed can be achieved. Laser-plasma arc hybrid welding has good adaptability to gap and misalignment in flat-plate butt welding, the maximum adaptive gap is 0.5 mm and the maximum adaptive misalignment is 1.5 mm.