In this paper,a new fluorescent carbon quantum dots（CQDs）were synthesized by one-step method using rapeseed and water as raw material.The experiments showed that potassium permanganate（KMnO4）could effectively quench the fluorescence of the CQDs.However,the fluorescence of CQDs-KMnO4 system restored reversibly in the presence of minocycline hydrochloride.Based on this principle,a new method was proposed for the determination of minocycline hydrochloride with the“off-on”fluorescence signal of rapeseed CQDs as a fluorescent probe.Under the optimum conditions,the linear range of the method was 5.0×10-7 mol/L to 1.0×10-5 mol/L with a correlation coefficient of 0.999 5 and a detection limit of 4.9×10-7 mol/L.The method was used in the determination of minocycline hydrochloride in samples with a recovery of 99.6%-100%.The mechanisms for CQDs fluorescence quenched by KMnO4 and recovered by minocycline hydrochloride were studied.