We presented a fast, specific, and sensitive DNA sensing system, which composed of a CdTe/Fe3O4 magnetic core-shell quantum dots (energy donor), a commercial quencher (BHQ2; energy acceptor), and a designed single strand Toxoplasma gondii DNA. The designed single strand Toxoplasma gondii DNA was applied to link the energy donor and acceptor, and target DNA was detected based on mechanism of fluorescence resonance energy transfer. The CdTe quantum dots, Fe3O4 magnetic nanoparticles, CdTe/Fe3O4 magnetic core-shell quantum dots, and sensing probe were step-wisely prepared. Properties of synthesized quantum dots were investigated by transmission electron microscopy, fluorescence spectrum, nano zeta potential and submicron particle size analyzer, and X-ray diffraction, respectively. Specificity and sensitivity of sensing probe was determined by measuring the recovery of fluorescence intensity. The obtained sensing probe with magnetic properties can be simply separated or concentrated from the hybridized solution with a common magnet. The resulting data revealed the sensing system was successfully fabricated, and which has high sensitivity and specificity.