A linear Hall-based eccentricity diagnosis method and detection system for a permanent magnet motor. First, three linear Hall elements are mounted in stator slots at the same space interval, respectively; second, analog signals output by the three-phase linear Hall are converted into digital signals by means of a digital signal processor, and the digital signals are converted into a quadrature signal by means of linear combination; then, a negative sequence signal and a sideband signal are extracted from the quadrature signal by means of a complex factor filter; then the amplitude of the negative sequence signal and the amplitude of the sideband signal are extracted by means of synchronous reference frame phase-locked loops as a static eccentricity indicator and a dynamic eccentricity indicator; finally, percentages representing the degrees of eccentricity are calculated from the static eccentricity indicator and the dynamic eccentricity indicator in the digital signal processor.