To accelerate the development of the laser welding technology of advanced high strength steel (AHSS), similar butt welding of 1.9 mm thick 22MnB5 and dissimilar tailored blank welding of 22MnB5 and Q235 are performed by using a fiber laser. The microstructure, hardness and tensile properties of weld joints are analyzed after the fiber laser welding (FLW). The results show that the microstructure of weld zone(WZ) mainly contains lathy martensite. Heat affected zone (HAZ) in 22MnB5 can be divided into three parts: quenched zone, incomplete quenched zone and tempered zone, and the last one is absent in Q235. The hardness distribution of weld joints is non-uniform, and the weld edge has the highest hardness. HAZ is very narrow and a soft zone exists in the 22MnB5 HAZ with the lowest hardness of 319.6 HV, while there is no soft zone in Q235. With the increase of welding speed, the martensite in WZ becomes finer, leading to the increasing of hardness. When the welding speed is 5 m/min, the highest hardness of the WZ attains 544.2 HV which is the highest of all the samples. The 22MnB5 samples for tensile test which are welded at the speed from 3 to 5 m/min are all broken in HAZ, and the elongation at break is only about 2%, which is obviously worse than that of base metal (8.9%).