The aim of this study is to develop a method for the determination of chlormequat (CCC) residues in grain and oil. The pretreatment by using QuEChERS and Gas Chromatography-Tandem Massspectrometry (GC-MS/MS) analysis were optimized. The samples were extracted from wheat flour, rice, corn, soybean, soybean oil, rapeseed, and rapeseed oil with acetonitrile and salted out with anhydrous magnesium sulfate, and sodium chloride, then cleaned up by a mixture of N-propyl ethylenediamine (PSA) and octadecyl silane (C18) adsorbents. The matrix effects of different substrates (wheat flour, rice, rapeseed, rapeseed oil) were investigated by derived mass spectrometry and matrix-matched calibration combined with external standards was used for quantitative analysis. The results showed a good linearity in the range of 0.05~2 μg/mL for CCC in different matrixes, with correlation coefficients (R2) of more than 0.9980. The limits of detection (LODs) and the limits of quantification (LOQs) of the method were 0.004~0.009 mg/kg and 0.01~0.03 mg/kg, respectively. The averagerecoveries at three spiked levels were 73.6%~99.1%, and the relative standard deviations (RSDs) were 2.34%~7.78% (n = 6). The method was efficient and sensitive, and satisfied the testing requirements for chlormequat residues in grain and oil samples.