Abstract: In order to study the influence of welding parameters and materials on the morphology of molten pool and keyhole, a coaxial monitoring system was built for fiber laser welding. The images of molten pool and keyhole were collected with 532nm and 808nm narrow band filter. Then, the 808nm laser illuminant was used to increase the light intensity of weld zone. The results indicate that, the detailed images of molten pool, keyhole and full penetration hole can be taken with 808nm narrow band filter under 808nm laser auxiliary illuminant. Under the same welding condition, molten pool and keyhole change in the stability, however, full penetration hole changes obviously with time. The change of weld pool is small. The change of small hole is dynamic and the fluctuation range is small. The dynamic characteristic of full penetration hole is obviously different from that of keyhole. The width of weld pool increases with the increase of laser power and decreases with the increase of welding speed. Coaxial monitoring of different material welding verifies the stability of monitoring system. This research provides theoretical instruction for real-time monitoring of laser welding.