A wireless siren anti-theft device mainly includes a host having a power-supply voltage-stabilizing circuit, an anti-theft coding and CPU circuit, a host control circuit, an emitting circuit, a host receiving circuit, and an I/0 socket; and a wireless siren being internally provided with a power-supply voltage-stabilizing circuit (21), an RF wireless receiving circuit (24), a decoding and CPU circuit (22), and an anti-theft voicing and driving circuit (23). The anti-theft coding and CPU circuit (22) generates Manchester anti-theft code having a Hi-Low ratio of 1:1, so that the wireless siren could quickly and accurately analyze received data code to emit precise warning sound.