The invention discloses a ground wire prompt device and an application method thereof, and related to the field of ground wire installation safety protection. The invention aims at solving problems that a conventional device cannot achieve the visual prompt of the state of a ground wire, and an accident is liable to be caused. Photoelectric diffuse reflection induction trigger time-delay switches are used for inducing whether there are ground wires or not. N photoelectric diffuse reflection induction trigger time-delay switches are corresponding to N indicating lamps. Each photoelectric diffuse reflection induction trigger time-delay switches and the corresponding indicating lamp are in series connection, thereby forming a series branch circuit. The N series branch circuits are in parallel connection. A power supply and the series branch circuits form a loop. N ground wire installation position cards are corresponding to the N indicating lamps, and are used for recording the installation positions of the ground wires. The method is used for recording the installation positions of the ground wires on the ground wire installation position cards after the ground wires are installed. The device can visually display the states of the ground wires, avoids misoperation, and is suitable for the prompt of the states of the ground wires.