Abstract: Three different types of drainage ditches,ecological ditch,control ditch #1 and control ditch #2 were built up in the field for study of their respective effectiveness in intercepting particulates in drainage and their mechanisms.It was found that the effectiveness of the ecological ditch removing N and P from drainage was manifested in N and P uptake by ditch plants,adsorption by substrates and uptake by plants in the filter box,reduced flow rate and silt settlement caused by intercepting dams in ditch,etc.Of the total N and P in the drainage of the summer experiment,68.30% and 78.45% were removed by ditch plants,1.05%and 5.05% by sediment.Of the total N and P in the drainage of the winter experiment,0.37%and 1.55% were removed by filter-box plants,10.82%and 37.94% by filter-box substrate.Moreover,the ecological ditch with interception dams was twice as much effective as the controls in extending the hydraulic retention time(HRT).