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[Objectives]The purpose of this study was to construct a magnetic nanoprobe and apply it to the fluorescent detection of atrazine. [Methods]The magnetic nanomaterial was firstly synthesized according to the hydrothermal method. A partially complementary DNA duplex was then constructed by the atrazine aptamer and a fluorescein-labeled DNA single strand and assembled on the magnetic nanomaterial. Upon the functionalization with the DNA duplex, the resultant fluorescent magnetic nanoprobe for the specific detection of atrazine was characterized by the ultraviolet spectroscopy and transmission electron microscopy. The atrazine-triggered release of the fluorescein-labeled DNA through the strong specific affinity between atrazine and its aptamer was confirmed by the polyacrylamide gel electrophoresis(PAGE)analysis. The release resulted in the unlocking of fluorescence quenching between the nanomaterials and the fluorescein, “turning” on the fluorescence for the sensitive quantitation of atrazine by the signal change of fluorescence spectroscopy. [Results]Atrazine was determined by fluorescence in the range of 0.01-20 μg·mL-1,with the correlation coefficient(R2)of 0.998. The detection limit was 8.17 μg·L-1. The nanoprobe showed high selectivity against atrazine compared with other pesticides and efficient anti-interference ability. The average recoveries of atrazine ranged from 95.48% to 102.03% with relative standard deviations(RSD)of 2.17% to 3.14% in the paddy water. The spiked recoveries of atrazine in paddy soil ranged from 94.79% to 100.66% with RSD of 3.40% to 4.72%. [Conclusions]The established fluorescent quantitative method for atrazine was simple but effective and had the sensitivity and accuracy to meet the requirements of pesticide residue analysis in the environment. [ABSTRACT FROM AUTHOR]