Fe-based alloys are prepared by the laser rapid forming technique. The influence of scanning speed on the microstructure and crystallization behavior of the formed Fe-based alloys is studied. The results show that, under a certain laser power, the large area of crystallization occurs both in the fusion zone and the heat affected zone with the increase of the scanning speed. The morphology and size of the precipitated phase in the fusion zone do not change obviously, however, the size of the precipitated phase in the heat affected zone decreases gradually. The laser rapid forming process is simulated by the Marc finite-element software, the thermal cycling curves in the fusion zone and the heat affected zone under different scanning speeds are obtained, and the reason why non-crystallization phase occurs for Fe-based alloys is analyzed.