Grassland is not only the material basis for developing livestock husbandry,but also the sensitive area which response to global climate change as well as the important water supply area for the Yangtze River and the Yellow River.Toxic and harmful grass is an essential part of grassland,and has significant and special ecological function.Toxic and harmful grass was considered as the"Green killer"of grassland and the"Invisible enemy"of grazing animals in traditional research.There is no doubt that it restricted the sustainable development of livestock production tremendously.Based on literature data analysis,combining with the related experimental data,in the present paper we discussed the ecological function of toxic and harmful grass in grassland agro-ecosystems from different angles.We conclude that toxic and harmful grass plays huge potential economic values in such as windbreak and sand-fixation,water conservation, maintenance of biological diversity,ornamental value,grazing management,livestock feeding and so on. We elucidated the mechanism of grassland degradation and the rules of toxic and harmful grass in the grassland agro-ecosystems,which will provide a theory basis for recovery of degradated grassland and grassland management.