The invention discloses a thermal conductive plastic alloy used for a radiator, a radiator and a preparation method. The thermal conductive plastic alloy comprises polybutene or polyisobutene, polyethylene, graphite powder, carbon fiber, thermal conductive carbon black, a thermal conductive reinforcing agent, a titanate coupling agent and stearic acid. The thermal conductive plastic alloy is subjected to granulation, then pipe drawing and injection molding are carried out, an inner water channel pipe and a connecting piece of an radiator are prepared, the inner water channel pipe is expanded into an inner hole of an aluminum wing pipe of the radiator to obtain a radiator column material or sheet material, the column material or the sheet material and the connecting piece are subjected to sweat soldering to prepare a radiator single sheet, and finally the radiator single sheets are subjected to sweat soldering to compose a radiator. The thermal conductive plastic alloy and the radiator are advantaged by good environmental protection and excellent heat radiation performance, are stable and durable, and have protruding characteristics of no fouling, no rusting, no corrosion, no cracking, no pollution, no deformation, no abnormal sound and no aging.