Abstract: According to the RAPD of Xanthomonas axonopodis pv. dieffenbachiae，specific primers were designed，and binding ability of carboxyl magnetic beads were tested. The system of optimization of immunomagnetic separation-PCR（IMS-PCR）protocol for detecting the Bacterial Blight of Anthurium were establisted. The results showed that the saturate absorption of 1 mg carboxyl magnetic beads to the polyclonal antibodys is 0.268 mg. The optimal concentration of immunomagnetic beads（IMB）is 0.566–0.741 mg ?mL^-1 when X. axonopodis pv. dieffenbachiae is captured. The detection sensitivity for X. axonopodis，by IMS-PCR which can reduce the inhibitory substances in reaction，is 10–100 cfu ? mL^-1. It is 100 times more sensitive than ordinary PCR at least. pv. dieffenbachiae

Key words: Authurium andreanum, Xanthomonas axonopodis pv. dieffenbachiae, IMS-PCR, sensitivity, saturation absorption, capture rate