In order to allocate biological measures for soil and water conservation reasonably,and to controlthe soil and water loss according to local conditions,this study focuses on the analysis of runoff and sedimentreduction effects under different types of forest and grass vegetation by a runoff plot experiment in a karstarea of Guizhou Province.Results show that most types of forest and grass vegetation in the study area hadexperienced three stages during the investigation time period(2008-2010):no effect,partial effect and remarkable effect on runoff and sediment reductions.By the end of 2010,the runoff reduction effect of different types of forest and grass vegetation was economic forests(their runoff reduction rates between 52.5% and64.3%)>mixed forest of poplar and portuguese cypress>ryegrass>portuguese cypress>white clover>poplar forest.The sediment reduction effect of different types of forest and grass vegetation was economicforests(their mean sediment reduction rate was 99.3%)>ryegrass>mixed forests of poplar and portuguesecypress>portuguese cypress forest>poplar forest>white clover.Allocation of forest and grass vegetationalso shows a great difference in runoff and sediment productions,therefore,type and allocation of forest andgrass vegetation should be considered simultaneously to achieve the best soil and water conservation effect.