The invention discloses a device for warning the deviation of a crane steel wire rope from a vertical angle. The device is formed by a device body, wherein the device body is formed by an angle detection mechanism and a warning mechanism; the angle detection mechanism comprises a multi-dimensional adjusting part, an angle warning unit formed by an angle judgment module and a pre-warning signal output module, and a power supply unit; the warning mechanism comprises a pre-warning signal receiving module, a buzzer and a power supply unit; after an angle judgment module receives a tilt angle signal transmitted through the multi-dimensional adjusting part, whether the tilt angle signal exceeds a preset value or not is judged; if the tilt angle signal exceeds the preset value, a start signal issent to the pre-warning signal output module, and otherwise, monitoring is carried out continuously; and the pre-warning signal output module demodulates and sends a pre-warning signal to the warningmechanism. The technical problem that when a crane steel wire rope used by an offshore platform is deviated from the vertical angle, a driver cannot know abnormalities in time is solved; and accordingto the device, operating personnel can be warned in time when the crane steel wire rope is deviated from the vertical angle.