Clavibacter michiganensis subsp. nebraskensis (Cmn) and Pantoea stewartii subsp. stewartii (Pss) are two plant pathogens that can cause tremendous agricultural economic losses. This novel method based on microsphere immunoreaction was developed for the simultaneous detection of Cmn and Pss in maize. This multiplex method was constructed based on microsphere immunodetection with fluorescent labels such as quantum dots (QDs) and R-phycoerythrin (R-PE) for the detection of Cmn and Pss. Captured QDs and R-PE serve as signal reporters for fluorescent readout. The principle of this method is based on a sandwich immunoreaction. Cmn and Pss captured by the microspheres were detected using flow cytometry. The limit of detection of this method was 10 times lower than the enzyme-linked immunosorbent assay (ELISA), and its analysis time (1 h) was much shorter compared with ELISA (6-8 h). The method, which has been proven to be an effective approach to multiplex detection of plant bacteria (Cmn and Pss as models), not only increased the varieties but also improved the sensitivity. The microsphere immunoreaction provides a universal method for the multiplex determination of microbes because of its high sensitivity, specificity, and speed. In the future, the method will be more fully validated in vivo to detect diversiform bacteria.