Design of a low-power micromachined ring-type flux- gate sensor with localized saturation cores has been made and optimized in this work. The design is accomplished by using the electromagnetic simulation software, MagnetTM, which is capable of establishing a quantitative connection between the sensor parameters and the geometrical parameters of the model. Using recently developed data extraction techniques, the design with low power (19 mW) and high sensitivity (590 V/T at 60 muT) can be achieved after a series of simulations. For comparison, an actual device has been fabricated with sensitivity of 650 V/T at 60 muT, power consumption of 14 mW. The good agreement between the simulation and the experimental results validate our new approach for the design of low-power fluxgate. In addition, measurements using a second-harmonics-based detection circuit have been performed so that the noise, stability, and perming effect of the fabricated device are explored.