A flow meter , comprising: a rotating structure , having a shaft , a rotating element , and a magnetic element ; wherein the rotating element can be driven by a fluid in a pipeline to rotate around the shaft, the magnetic element is arranged on the rotating element with two magnetic poles parallel to a tangent line of rotating circle of the rotating element; a sensing element , separated from the rotating structure by a distance, and comprising a first sensing unit and a second sensing unit , which respectively senses a magnetic field of the magnetic element in a first direction and a second direction to generate a first magnetic field component signal and a second magnetic field component signal; and a processing circuit , connected to the sensing element , and characterized in that it generates an angle (θ i ) of the rotating structure by performing an arctangent operation on the first magnetic field component signal and the second magnetic field component signal, in that the processing circuit further calculates magnetic field intensity of the magnetic element according to the first magnetic field component signal and the second magnetic field component signal, in that the processing circuit stored an upper bound of the magnetic field intensity and a lower bound of the magnetic field intensity in advance; and in that when the magnetic field intensity is higher than the upper bound, the processing circuit produces an information of abnormal external magnetic field interference; and when the magnetic field intensity is lower than the lower bound, the processing circuit produces an information that the rotating structure is damaged. a rotating structure , having a shaft , a rotating element , and a magnetic element ; wherein the rotating element can be driven by a fluid in a pipeline to rotate around the shaft, the magnetic element is arranged on the rotating element with two magnetic poles parallel to a tangent line of rotating circle of the rotating element; a sensing element , separated from the rotating structure by a distance, and comprising a first sensing unit and a second sensing unit , which respectively senses a magnetic field of the magnetic element in a first direction and a second direction to generate a first magnetic field component signal and a second magnetic field component signal; and a processing circuit , connected to the sensing element , and characterized in that it generates an angle (θ i ) of the rotating structure by performing an arctangent operation on the first magnetic field component signal and the second magnetic field component signal, in that the processing circuit further calculates magnetic field intensity of the magnetic element according to the first magnetic field component signal and the second magnetic field component signal, in that the processing circuit stored an upper bound of the magnetic field intensity and a lower bound of the magnetic field intensity in advance; and in that when the magnetic field intensity is higher than the upper bound, the processing circuit produces an information of abnormal external magnetic field interference; and when the magnetic field intensity is lower than the lower bound, the processing circuit produces an information that the rotating structure is damaged. <EOS>