Abstract: A method for the detection of four organophosphorus pesticide residues—dichlorvos, malathion, triazophos, and chlorpyrifos—in grain was developed based on GB23200.113−2018. Rice grain was used as the experimental material, and samples were processed using two different pretreatment methods: the conventional QuEChERS method（carried out at room temperature before and after extraction, as well as during purification）and an improved QuEChERS method（involving lower sample temperatures throughout the process）. The analysis was conducted using gas chromatography-tandem mass spectrometry（GC-MS/MS）in multiple reaction monitoring（MRM）mode to evaluate the linear relationships, limits of quantification, recoveries, and precision of four organophosphorus pesticides. The findings indicated that all four pesticides demonstrated excellent linear relationships across the concentration range of 0.005–0.5 mg·L⁻¹, with correlation coefficients（R²）exceeding 0.9999. The detection limits and limits of quantification were found to comply with the standard requirements. When analyzing residues of malathion, triazophos, and chlorpyrifos at spiked levels of 0.02, 0.1, and 0.5 mg·kg⁻¹, there was no significant difference observed between the two methods in terms of detection effectiveness. Both the traditional and improved QuEChERS methods met the standard requirements for reproducibility, detection limits, and recovery rates. However, for dichlorvos, the improved QuEChERS method showed a recovery rate range of 75.8%–90.4%, which was notably higher than the recovery rate of the conventional QuEChERS method（55.8%–62.4%）. In summary, the analysis suggests that the improved QuEChERS method, when combined with GC-MS/MS, offers superior accuracy and recovery rates, making it a more suitable choice for detecting the four organophosphorus pesticide residues in rice grain.