A novel method was developed for the determination of trace benzenes in water samples by on-line thermal desorption-gas chromatography after solid phase extraction on Fe/SiO2/PDMS particles bed column.The solid phase extraction column was prepared by filling prepared Fe/SiO2/PDMS particles into quartz tube.The adsorbed benzenes on the column was thermally desorbed and directly introduced into gas chromatography for separating and determing.Several factors affecting the extraction and separation efficiencies were investigated and optimized. Under the optimal conditions，the calibration curves of benzenes were linear in the range of 0.1-20 ng/L，with corrrelation coefficients(r) of 0.999 2-0.999 6 and detection limits(S/N=3) of 0.03-0.05 ng/L.The relative standard deviations(RSD，n=11) for 1 ng/L benzenes were in the range of 2.0%-4.4%.The presented method was sensitive and accurate，and was successfully applied in the determination of benzenes in water samples.