A coating apparatus includes a deposition case, a reaction assembly, two precursors, a target, and a driving assembly. The deposition case includes a housing defining a cavity for receiving workpieces. The reaction assembly receives in the cavity and includes an outer barrel, an inner barrel, a plurality of nozzles, and a plurality of pipes. The outer barrel includes a main body and two protruding bodies. The main body and the inner barrel cooperatively define a first room therebetween. Each protruding body defines a second room communicating with the first room. The inner barrel defines a third room. The nozzles extend from the main body and communicate with the first room. The pipes extend from the inner barrel and communicate with the third room. The precursors receive in the second rooms. The target receives in the third room. The driving assembly drives the housing to rotate relative to the reaction assembly.