The invention relates to a copper plating liquid and process for direct cyanide-free acid copper plating on a steel substrate, belonging to the technical field of copper plating. The copper plating liquid comprises copper sulphate, sulfuric acid, deionized water, chloride ion, a desmutting agent, an activator and a complexing agent, wherein concentrations of the copper sulphate, the sulfuric acid, the chloride ion, the desmutting agent, the activator and the complexing agent are 50 to 200 g / L, 20 to 80 g / L, 0.02 to 0.08 g / L, 5 to 50 g / L, 10 to 100 g / L and 10 to 100 g / L, respectively, and the weight of deionized water is 400 to 900 g. Compared with the prior art, the invention has the following advantages: the copper plating liquid can realize direct copper plating on the steel substrate without pre-plating; an obtained plating is fine and shiny and has good bonding strength; after continuous electroplating on a steel band copper plating production line for 10 years, the copper plating liquid can still be normally used; and the copper plating liquid can be used for continuous electroplating of steel bands, steel wires and steel pipes and for rack plating, barrel plating and the like of steel members.