Abstract: The surface of 45 steel cold drawn flat keys were scanning treated by nanosecond pulsed laser with a wavelength of 355 nm.The samples with different process parameters were prepared, and the surface characteristics were investigated.The results show that the microhardness increases from 301.7 HV0.2 to 442.8 HV0.2 before and after laser scanning processing, nearly 50% increase comparing with that of an original surface.The thickness of the laser hardening layer is about 30 μm.The roughness of the laser scanning surface can be reduced by post-vibration polishing without decreasing the surface hardness of laser scanning.