A metal-based/diamond laser composite coating preparation method includes: first selecting high-hardness metal powder and diamond powder of a proper grain size and shape; then uniformly mixing the high-hardness metal powder and diamond powder via a ball-milling method; and finally preparing a composite coating on a substrate by synchronously combining laser texturing technology, laser thermal treatment technology and cold spraying technology. The thickness of the composite coating is greater than 1 mm, and the volume content of diamond in the coating is greater than 45%. A metal-based/diamond laser composite coating is also provided.