A ratiometric fluorescent probe (CQDs/Eu3+) was constructed with carbon quantum dots (CQDs) and europium ions (Eu3+) as fluorophores for the detection of ciprofloxacin (CIP). At excitation at 395 nm wavelength, CQDs/Eu3+ has an intense blue fluorescent peak at 459 nm, and a weak red fluorescent peak at 616 nm in the presence of CIP. The fluorescence (FL) intensity of CQDS at 459 nm is enhanced based on the antenna effect. The major factors like ratio of CQDs and Eu3+, response time and stability were optimized, The results show that the ratio fluorescent probe has a specific recognition ability for CIP. And there is a linear relationship between the fluorescence intensity ratio (F459/F616) and concentration of CIP (0-7×10-6 mol/L), and the lowest detection limit for CIP is 0.3×10-6 mol/L. This probe can be used for the detection of CIP in milk under the addition of CIP.