The invention discloses a high-rise building shape steel cantilever scaffold and unloading platform deflection safety monitoring pre-warning device.The device comprises an adjustable base and an alarm device, wherein the adjustable base is fixedly installed at the end of a cantilever beam or unloading platform, and the alarm device is arranged on the adjustable base.The alarm device comprises an installation shell, a tilt switch, an alarm device switch and an alarm prompt mechanism, wherein the tilt switch, the alarm device switch and the alarm prompt mechanism are arranged in the installation shell.A pin of the tilt switch is connected with the alarm device switch through a circuit.The alarm device switch is connected with the alarm prompt mechanism through a circuit.The adjustable base and the installation shell are both provided with a leveling instrument.The pre-warning device is installed at the end of the cantilever beam or the unloading platform, so that the change angle of the tilt switch in the alarm device and deflection change of the cantilever beam or the unloading platform are consistent, the tilt switch is triggered when the cantilever scaffold or the unloading platform bears loads exceeding a scheme to trigger the alarm device, and accordingly the problem about safety real-time monitoring of a cantilever scaffold or an unloading platform of a high-rise or super high-rise building is effectively solved.