The invention discloses a coating device and a coating method for an internal catalyst layer of an oxygen sensor. The coating device comprises an external sealing layer which is in close fit with the inner wall of a zirconium tube of an oxygen sensor; the coating device also comprises a compressed air channel layer which is concentric with the external sealing layer, an annular hollow space between the external sealing layer and the compressed air channel layer is a backflow channel, and a circular hollow area surrounded by the compressed air channel layer is a channel filling compressed air into the backflow channel; and the front end of the compressed air channel layer is of an open structure. According to the device and the method, platinum paste can be uniformly coated at a position on the zirconium tube of the oxygen sensor and corresponding to an external catalyst layer in a compressed air blowing mode so as to form the internal catalyst layer corresponding to the external catalyst layer; and according to the coating device and coating method disclosed by the invention, the internal catalyst layer can enable an oxygen sensor to have a good electrical property, and in the process of coating, the application amount of platinum paste is reduced, and the cost of the oxygen sensor is lowered.