In this work， the detection method of cyanamide in fruits and vegetables was established， using a synthesized rhodamine B-N-hydroxy succinimide (RBS) as the new pre-column derivatizing reagent. After extracted with ethyl acetate and derivatized with RBS， the samples were determined by high performance liquid chromatography-mass spectrometry. The results showed that the reagent RBS had advantages of detection sensitivity for mass spectrometry and was highly efficient and specific in the derivatization reaction of cyanamide. In addition， a better linear relationship was shown when the concentration of cyanamide was 0.005-5 mmol/L， with the correlation coefficient was 0.9969. It was found that the detection limits and quantification limits of this method were 0.001 mmol/L and 0.0025 mmol/L， respectively. The standard recovery rate of samples was in the range of 77.56% - 105.21% and the relative standard deviation was among 1.88% - 4.04%. This method meets the requirements of analysis， with good selectivity， high sensitivity and low detectable limit， and is suitable for the determination of cyanamide residues in fruits and vegetables.