Federated learning system using synonym

A federated learning system with synonym includes a moderator and a plurality of clients. Each client includes an encoder encoding private data into a digest. The client trains a client model according to the private data, the digest and a general model, and sends the digest and a client parameter of the client model to the moderator. The moderator is communicably connected to every client and includes a synonym generator. The moderator sends the general model to every client and determines an absent client of the plurality of client. The synonym generates a synonym of the digest corresponding to the absent client. The moderator trains a replacement model according to the synonym and the digest corresponding to the absent client device, performs an aggregation to generate an updated parameter to update the general model according to a replacement parameter of the replacement model and the client parameter of every client except the absent client.