The invention discloses copper welding paste for braze welding, a preparation method of the copper welding paste for braze welding and the application of the copper welding paste for braze welding. The copper welding paste for braze welding comprises 67wt%-92wt% of brazing filler metal, 8wt%-33wt% of pasty fluid and brazing flux of which the mass is 0-5% that of the brazing filler metal, wherein the brazing filler metal comprises Cu and/or one or more types of Cu alloy, the brazing flux comprises any one or more than two components of CaF2, KF, NaF, BaF2, sebacic acid, succinic acid, lauric acid and boric acid, and the pasty fluid comprises a solvent, a thickening agent, a rheological agent, an antifoaming agent and an activating agent. When the copper welding paste prepared through the method is applied before braze welding, the copper welding paste has good thixotropy, collapse resistance and fluidity; after braze welding, a part has high joint strength, a weld joint is plump and free of residues, and the part does not need cleaning; the copper welding paste can be widely applied to welding automobile pipe fittings, copper-based heat dissipation assemblies and stainless steel parts.