The invention discloses a blade heavy metal content detection method for correcting moisture content based on CN element ratio. The method comprises the following steps: 1) obtaining blade samples different in heavy metal content, and pretreating the samples; 2) detecting heavy metal content in the samples by a standard method; 3) collecting spectral lines on different positions of the sample by laser-induced breakdown spectroscopy; 4) pretreating the obtained spectral signal; 5) extracting LIBS spectral line peak strength corresponding to heavy metal element and CN element; 6) establishing a calibration model by taking the heavy metal content of the sample as output Y and the measured strength of heavy metal element and CN element as input; and 7) collecting the spectral lines of a to-be-detected sample, extracting the LIBS spectral line peak strength of the heavy metal element and CN element in the pretreated spectral signal, and inputting into the calibration model to obtain the heavy metal content. The method disclosed by the invention can correct moisture content in a sample to eliminate influence of moisture content in the sample on heavy metal detection and improve the detection precision.