In this paper,a fluorescent probe for the dectection of cimetidine was fabricated based on fluorescence resonance energy transfer effect(FRET) between carambola carbon quantum dots(CB-CQDs) and silver nanoparticles(AgNPs).The CB-CQDs with high fluorescence intensity and good luminescence performance were synthesized by hydrothermal method using natural fruit carambola as the only raw material,which morphology and properties were characterized by ultraviolet-visible spectroscopy(UV-Vis),infrared spectroscopy(FTIR),transmission electron microscopy(TEM) and fluorescence spectrometry(FL),respectively.It was found that,when AgNPs was added into a pH 6.0 Britton-Robinson buffer solution containing CB-CQDs，the fluorescence signal of CB-CQDs at λex/λem=319 nm/397 nm was gradually quenched through the FRET effect,in which CB-CQDs and AgNPs acted as fluorescence donor and fluorescence acceptor,respectively.While in the presence of cimetidine,the fluorescence signal of CB-CQDs was restored and fluorescence signal “turned on” again,forming an “off-on” cimetidine sensor,and the basic mechanism was further discussed.Under the optimized conditions,there was a good linear relationship between fluorescence recovery value(ΔIF) and cimetidine concentration in the range of 9.0×10-8-1.0×10-6 mol/L,with a correlation coefficient(r) of 0.998 6.The detection limit was calculated to be 1.9×10-8 mol/L based on the 3σ/k principle.This method was successfully applied to the detection of cimetidine in real samples with satisfactory results.