The method for determination of dicyandiamide in farm products was developed by performance liquid chromatography-electrospray ionization tandem mass spectrometry( HPLC-MS / MS). Deuterium substituted reagent were used as internal standards and added to the sample before extraction. The sample was extracted with aminated acetonitrile,concentrated with syncore analyst,and cleaned up by hexane. The mass spectrometer was operated in the positive ion mode using select reaction monitoring for qualitative and quantitative analysis of dicyandiamide. The limits of detection for dicyandiamide were 10 μg / kg and limits of quantization were 40 μg / kg. The correlation coefficient of linear calibration curve was over 0. 999 within the dicyandiamide concentration range 10 ~ 1000ng / ml. The average recoveries for dicyandiamide were 94. 8% to103. 3%. The method is simple,rapid,reliable,stable and sensitive. It can meet the requirements of the daily work for the determination of dicyandiamide in agriculture products.