In the present study, spatial and temporal distribution of methyl mercury in Hongfeng reseivoir were investigated by distillation followed by aqueous phase ethylation, precollection on a Tenax, isothermal gas I'hromatog-raphy and cold vapor atomic fluorescence detection. Total methyl mercury (TMeHg) ronrentralions have tio discernible difference (0.05 to 0. 33ng/L) in springt autumn and winter. In spring, the methyl mercury in the inflows was important source of methyl mercury in reservoir. In summer, methyJ mercury concentration increased significantly,and the highest value was up to 0. 923ng/L in the hypolimnion. The spatial distribution in summer suggested methylation in the water column and sedimentation of particle were responsible for the evaluated methyl mercury other than the release of sediment. There was a discernible negative relationship between methyl mercury and dissolved ox>gen(r--0. 81,n= 78), In spring, autumn and winter, the proportion of dissolved methyl mercury (DMeHg) was lower than that of particulate methyl mercury, but mosl of methyl mercury was dissolved in hypolimnion in summer. The outflow of reservoir was rich in methyl mercury in summer, and the value was 5. 5 limes higher than that in the infows. MeHg-enriched water from anoxic hypolimnia in reservoir also was discharged and potentially transported downstream where it could affect the ecosystem below the reservoir.