Design, fabrication, characterisation and calibration of a three-axis, ring-core, second harmonic fluxgate magnetometer is described in detail. Owing to the good material selection, precise structural fabrication, and high-performance processing unit, in addition to implementation of a novel and effective calibration algorithm, the sensor features good characteristics such as 0.1° non-orthogonality, 0.03% accuracy and 0.08% linearity. The power consumption of the fabricated sensor is 0.7 W. We have also compared the noise level of two types of commercial ring cores and shown that the experimental findings confirm our expectation about the noise level of the cores. In addition, a novel calibration method using the neural network was used to reduce errors of the fluxgate sensor.