A method for transmitting data in a wireless system, wherein the wireless system includes a server, a relay device, and at least one appliance. The method includes that the relay device is connected to the server through an internet; determine whether there is a state information sent from the appliance being stored in the relay device; if so, send the state information to the server; otherwise, send a first interactive command to the server, wherein the first interactive command corresponds to a situation that there is no state information being stored in the relay device; send a second interactive command to the server, and then interrupt a connection with the server, wherein the second interactive command requests the server to interrupt a connection with the relay device. Whereby, the server could determine whether the relay device transmits data normally or not, ensuring the reliability of data transmission.