Timely and accurate monitoring of leakage current is the foundation for achieving insulation monitoring and fault early warning of electrical equipment and ensuring the safe and stable operation of the power grid.With the wide application of renewable energy and power electronic equipment，the measurement of leakage current needs to achieve mA-level accurate measurement without affecting the normal operation of equipment.Tunneling magnetoresistance （TMR） technology senses the magnetic field generated by the current to be measured through the quantum tunneling effect.Its unique material structure endows it with ultra-low power consumption and weak current detection capabilities，providing core support for the sensor design in this paper.This paper first constructs a current sensing structure suitable for mA-level non-contact measurement based on the working principle of TMR.Second，to address the sensitivity temperature drift problem of TMR sensors in complex temperature environments，an innovative software compensation method based on cubic spline interpolation is proposed.By fitting the output data of the sensor at different temperatures，a continuous sensitivity compensation curve is obtained，significantly improving the temperature stability of the sensor.The magnetic ring and signal processing circuit of the sensor are optimized and designed.Finally，through the development of a prototype for experiments，it is proved that within the current range of ± 250 mA，the designed high-performance non-contact mA-class TMR current sensor can accurately measure the current at 0.2%FS，with a temperature drift coefficient as low as 106.3 ppm/℃，which is approximately 73% lower than that in the traditional hardware compensation method （387.9 ppm/℃）.It significantly suppresses the influence of environmental temperature，and the sensitivity is 9.994 V/A，meeting the requirements of weak current measurement in fields such as safe operation of power grids and insulation detection.