The invention discloses a magnetic coupling radio frequency identification tag circuit applying a loop coil antenna. According to the invention, a clock recovery circuit and a demodulation circuit, which are suitable for a high direct current component and alternating coupled oscillation signals, are adopted by a tag, thereby not only being capable of forming a close-range conventionally applied magnetic coupling radio frequency tag directly together with the coupling loop coil antenna, but also being capable of realizing remote applications by being combined with a diode and a direct-current power supply through the coupling loop coil antenna.