Abstract: Objective To establish a simple, rapid, accurate and reliable method of gas chromatography-mass spectrometry (GC-MS) with water extraction in order to determine the paraquat in biomaterial. Method The biomaterial was firstly pre-treated by using water as reagent to extract paraquat, and then GC-MS was employed to determine these samples. The retention time of the paraquat in total ion current (TIC) and the characteristic fragment ions of paraquat in mass spectrogram were taken as qualitative basis. Result The method demonstrated several advantages: simple sample pre-treatment, little consumption of organic reagents, less background interference, good separation effect, and fast analytical speed. The retention time was 6.674 mins and the characteristic fragment ions was 156 (m/z =156) . The recovery rate was 91.42% and the relative standard deviation (RSD) of the intra-day and the inter-day were 4.83% and 6.87% respectively. The lowest limit of detection (LLOD) was 0.005mg/mL. Conclusion The method can be applied to determine the paraquat in biomaterial of forensic toxicological analysis.