A sludge-free method and apparatus for treating wastewater by recovering copper to reduce sludge is described, which comprise treating wastewater with copper by heavy metal chemical precipitation, and then getting sludge with high concentration of copper; leaching the sludge in an acid tank containing 1N sulfuric acid solution and separating into liquid and solid to form copper containing solution and residue, in which; the solution contains 18-39% copper, and a cryogenic crystallization method is used to produce high economic value compound -copper sulfate crystal. Furthermore, the produced residue can be recycled to function as a precipitant to be directly added into a fast mixing tank of the wastewater treatment process. Through the application of this invented method, a solution with high copper content or copper sulfate crystal after cryogenic crystallization can be obtained and at the same time the produced residue can be recycled to substitute the precipitant used in the wastewater treatment process. This invention provides series of processes with advantages of converting copper containing wastewater into valuable metal material, reducing wastewater, sludge treatment units and greatly decreasing treatment cost to achieve sludge-free target.