In this paper, we presented the basic principle and fabrication method of an integrated optical waveguide current sensor based on a micro-ring resonator coated with Fe₃O₄ magnetic nanoparticles. In the alternating magnetic field generated by the measured current, Fe₃O₄ nanoparticles produce energy loss, and then the temperature changes. As a result, the refractive index of the waveguide varies. Current sensing can be realized by monitoring the drift in the resonance wavelength output from the micro-ring resonator. We reasonably designed the key parameters by the finite difference time domain method to obtain a wide-range and high-quality micro-ring resonator and thus prepared current sensors with different micro-ring radii. The theoretical and experimental results show that the drift in the resonance wavelength is proportional to the square of the current amplitude and frequency respectively when the measured current amplitude is 0 to 0.5 A and the frequency is 0 to 60 kHz. Besides, with the decrease in the micro-ring radius, the detection range of the sensor increases and the sensitivity drops. This paper can provide a theoretical basis for the integrated miniature current sensors and promote the development of silicon-based photoelectric sensors.