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Non-destructive defect testing with a passive magnetic detection technique is crucial for magnetic materials, which can be exempt from the extra excitation magnetic field or developer replenisher contamination. We demonstrate a novel and high-resolution non-destructive defect testing of a magnetic turbine blade in the earth's magnetic field using a passive magnetic detection technique and a precisely controlled experimental system. The variation in the turbine blade's magnetic field, measured by a three-dimensional and sensitive sensor mounted on a translation system, was numerically processed and visually demonstrated according to the experimental data. The element differential method was used for simulation and analysis, and we found that a feasible distance and an optimal signal-to-noise ratio can be reached at a testing distance of h = 1 mm. The magnetic characteristics obtained experimentally are in good agreement with those of the sample defect spots with the best spatial resolution of 0.1 mm. The major sources of systematic errors including dead zones and sensor orthogonality were also briefly discussed along with the possible solutions. [ABSTRACT FROM AUTHOR]