Abstract: To study the persistence of slope protection effect,in situ pull-out test was conducted to test four herbs of one-year-old to four-year-old: Achnatherum splendens,Agropyron trachycaulum,Elymus nutans,Leymus secalinus.The results indicate that the average pull-resistance,root fibril quantity,root diameter and root length increase with the time of growth.There exist the following relations: a power relation between average pull-resistance and time of growth for Achnatherum splendens,a exponential relation for Agropyron trachycaulum,Elymus nutans and Leymus secalinus,a logarithm relation between average root fibril quantity and time of growth for four herbs,a power relation between average root diameter and time of growth for Achnatherum splendens,and a logarithm relation for Elymus nutans and Agropyron trachycaulum,and for Leymus secalinus.There exists a logarithm relation between average root length and the time of growth, a linear relation for Agropyron trachycaulum and Leymus secalinus and a power relation for Elymus nutans.