Using Co-based alloy coating powder containing certain amount of nano-Al powder, the ceramic phase reinforcing Co-based alloy coating was produced by pulse laser overlapping in-situ synthesis on the surface of Cu-Cr alloy for crystallizer. The structure and forming mechanism of the coating were studied by means of optical microscope , X-ray diffraction (XRD), scan electronic microscope and micro-hardness tester. The results show that the ceramic phase reinforcing Co-based alloy coating is produced on the surface of Cu-Cr alloy and the interface get metallurgical bonding between the Co-based alloy coating and Cu-Cr alloy substrate by using the optimized technological parameters of laser (current of 175 A, frequency of 15 Hz, pulse width of 3 ms, scan rate of 4.0 mm/s) and overlapping rate (20%～25%). The maximal size of the ceramic particles by in-situ synthesized is about 3 μm. Most of the ceramic particles are regular shape as ball and dispersive distribution. The principle of the Co-based alloy forms crystalline is that the ceramic phase as the center promotes the liquid Co-based alloy around it to be crystalline, and the crystallinic alloy enwrapps the ceramic phase. This process controls the aggregation of the ceramic phase, which causes the particles dispersive and small. The hardness of Co-based alloy coating (300HV) was improved obviously compare with that of Cu-Cr alloy substrate (94HV).