Objective:To establish a chemiluminescence immunoassay method for free metanephrines measurement in plasma, and verify its performance.Methods:The samples (calibrator, plasma, and quality control sample) were extracted and acylated, the processed analyte samples were then competed with the immobilized specific antigens of metanephrine (MN), normetanephrine (NMN) respectively, to combine specific antibodies marked by Horseradish Peroxidase (HRP), the immobilized antigens-antibody-HRP immune reaction product was then formed through the immune reaction, which could be detected through measurement of HRP catalytic substrate luminescence. Performance verification was performed using specificity, sensitivity,precision,thermally accelerated stability, and accuracy metrics.Results:The established detection methods for MN and NMN have no obvious cross-reactions when detecting multiple structural analogs; the limit of blank, limit of detection and functional sensitivity of the MN detection reagent was 10.51, 21.15 and 25.76 ng/L, and the performance of the NMN detection reagent was 11.54, 28.43 and 31.29 ng/L; the coefficients of variation of the detection reagents for MN and NMN were 2.41%-5.38% and 1.61%-3.22% respectively; the accelerated stability test of the two detection reagents showed that the reagents could be stored stably for 1 year at 2-8 ℃; and the measurement results of this method can be traced to the mass spectrometer.Conclusion:In this study, a chemiluminescence immunoassay detection method for free metanephrines in plasma is successfully established.