The invention provides a conventional island pipe wall thinning detecting device and method for a nuclear power plant. The device includes a temperature measuring probe which is arranged at an outer pipe wall surface of a to-be-detected pipe and is used for measuring the temperature of the outer pipe wall surface of the to-be-detected pipe, a middle storage device used for receiving and storing atemperature measuring signal transmitted by the temperature measuring probe, and a portable mobile terminal which is plugged on the middle storage device and is used for receiving the temperature of the outer pipe wall surface of the to-be-detected pipe from the middle storage device and acquiring thickness of the pipe wall of the to-be-detected pipe based on the heat conduction condition. The device is advantaged in that dismounting temperature insulation equipment and setting scaffolds can be omitted, a lot of human resources are saved, high efficiency is achieved, one-time investment is achieved, cost for calibration of the temperature measuring probe and periodic maintenance of the mobile terminal is only required, and economic property is further achieved.