A new analytical method has been developed to detect three kinds of DNA simultaneously based on magnetic beads and color-encoded plasmonic nanocrystals. Magnetic beads modified with capture DNA are employed to collect the specific target DNA, and color-encoded plasmonic nanocrystals are applied to signal the target through DNA hybridization. As a proof of concept, three types of representative metal nanocrystals of gold nanoparticle (AuNP), gold nanorod (AuNR), and gold/silver nanoparticle (Au/AgNP) were employed to signal three dissimilar virus-related protective antigen genes, Ebola virus (EV), Variola virus (VV), and Bacillus anthracis (BA), respectively. Detection limits of 0.5–3 fM were obtained showing the high sensitivity for DNA detection. The microscopic discrimination of the encoded nanoparticles allows simple, rapid, accurate, and cost-effective detection of multiple DNA molecules, indicative of the potential in practical applications.