The invention provides a drainage cover assembly, a water pan and an air conditioner, and relates to the technical field of refrigeration equipment. The drainage cover assembly comprises a drainage cover body and a one-way conduction structure, the drainage cover body provides a first end and a second end which are opposite to each other, the first end and the second end are provided with a connecting structure used for being connected with a drainage port respectively, a drainage channel is formed in the drainage cover body, one end of the drainage channel communicates with the first end, a connecting pipe structure is arranged at the other end of the drainage channel, and the one-way conduction structure is used for controlling the drainage channel to be in one-way conduction from the first end to the connection pipe structure. According to the drainage cover assembly, the first end or the second end of the drainage cover body can be selected to connect with the drainage port, so that the drainage cover body is switched between an adapter and a sealing cover, the integrated design of the adapter and the sealing cover is realized, the problem that only the adapter or the sealing cover can be mounted on the drainage port at the same time is avoided.