Non-point source pollution which was caused by the agricultural exploitation activities in riparian floodplain has more distinct and more direct effects on the water quality of rivers than that in other places.In this paper,the characteristics of rainfall and runoff in Mengjin floodplain of Yellow River from 2006 to 2007 were studied.The agricultural exploitation types on the impact of the runoff and pollution were discussed.The results show that the uniform rainfall generates runoff the most likely in three rainfall types.Rainfall erosivity(R) is an important factor of the amount of runoff.When R is lower,different types of vegetation have little impact on the amount of runoff.However,under the condition of R>19.00(dryland farming) and R>33.00(plantation),the types of vegetation have great influence.When the floodplain was developed into the dryland farming,about 45.0 kg/hm2 of particulate matter,0.904 kg/hm2 of organic matter,0.443 kg/hm2 of nitrogen,0.050 kg/hm2 of phosphorus can be produced,which are double compared to those of the floodplain being developed into the plantation.