Abstract: Researches on the experimental closing of hillsides to promote afforestation were made by the Beijing Research Group on Secondary Forest in Gushiyu of Miyun County, Beijing in 1984. The concrete research method has been described in the issue N.2, 1987 of this journal.In the five-year sresearches, reexamination was taken three times. These reexaminations proved that the vegetation coverage, the biomass of shrubs and herbs and the diversity index had increased. Four kinds of plots regenerated well. Two kinds of plots on the drougt sunny slopes regenerated badly, but the baks introduced there have been growing well result. Besides, an experiment on transplanting the roots of aspen was made by the Research Group.