A method for transmitting data in a wireless system, wherein the wireless system includes a first server, a second server, a relay device, and at least one appliance. The method includes that the relay device is connected to the first server through a network; determine whether the relay device stores a state information sent from the appliance; if so, send the state information to the first server; otherwise, send a first interactive command to the first server; receive a data sent from the relay device by the first server, and transmit it to the second server for subsequent process; the relay device sends a second interactive command to the first server, and then interrupt a connection with the first server. Whereby, the first server could determine whether the relay device transmits data normally or not by individually communicating with the relay device, ensuring the reliability of data transmission.