Abstract: Bioturbation effect of benthic fish,e.g.Misgurnus anguillicaudatus,on nitrogen dynamic in paddy field surface water and its mechanism was investigated through a simulation experiment analyzing comparatively nitrogen contents in waters with and without Misgurnus anguillicaudatus.Misgurnus anguillicaudatus showed strong bioturbation effect.Throughout the experiment,NH⁺₄-N and NO^-₃-N concentrations remained higher in the bioturbation group than in the control group,while NO^-₂-N concentration did not show any obvious rules.In the early stage of the experiment NH⁺₄-N/TN ratio was higher in the bioturbation group than in the control group,while in the middle and late stages of the experiment it turned reversely.DIN/TN ratio was markedly higher in the bioturbation group than in the control group.Misgurnus anguillicaudatus bioturbation increased remarkably DIN and TN concentrations in paddy field surface water.