【Objective】Planting medicinal plants is an effective way to improve economic benefit of forest lands. However, it is important to take into account whether leachates from medicinal plants would have allelopathic effects on decomposition of forests litter and soil, and it is also the key to selection of medicinal plant species to build a scientific and reasonable compound system of forest-medicinal plants.【Method】In this paper, a Populuspurdomii forest typical of the Qinling Mountains and nine species of medicinal plants ( Taraxacummongolicum, Corydalis bungeana, Menthahaplocalyx, Houttuyniacordata, Asarumsieboldii, Lonicera japonica, Nepetacataria, Gynostemmapentaphyllum and Prunella vulgaris ) common in the area were cited as objects in the study, a simulation experiment was carried out on litter decomposition by spraying leachate in water-extraction solution from stems and leaves of the medicinal plants, to study effects of the leachates on litter decomposition, nutrient release and soil enzyme activity. The sampling area in this experiment is the Houzhenzi Forest Farm of Zhouzhi County in the QinlingMountains of Shaanxi. The decomposing bag method was used in the indoors litter decomposition experiment with constant temperature and humidity and the experiment lasted for six months. During the experiment, leachate from the litter of medicinal plants was sprayed once every two weeks, and the decomposing bags were retrieved five times (in the first, second, third, fifth and sixth month after the start of the decomposition experiment), soil samples collected three times (in the first, third and sixth month after the start of the decomposition experiment), to determine decomposition rate, nutrient release and soil enzyme activity. At the same time, GC-MS was used to analyze chemical substances in the medicinal plants leachate.【Result】Turnover period and half-life of the decomposition of P. purdomii litter was extended by 230% and 29%, respectively, in the treatment using T. mongolicum leachate, by 67% and 23% in the treatment usingM. haplocalyx leachate, and by 120% and 34% in the treatment using H. cordata leachate. And leachate from all these three species of medicinal plants displayed significant inhibitory effects on nutrient release and soil enzyme activities during decomposition of P. purdomii litter. In order to facilitate the analysis, the experiment was divided into three phases; i.e. early (first month), middle (second to third months) and later (fourth to sixth months) phases. The inhibitory effects were significant on the release of nitrogen, copper, zinc and manganese in the early and late phases in all the three treatments, on the release of potassium in the middle and late phases, on the release of carbon in the early, middle or late phases, and on the release of phosphorus in the early or late phases. And the inhibitory effects were also observed on the activities of invertase, dehydrogenase and protease in the early or middle phase, on the activities of carboxymethylcellulase, polyphenol oxidase and phosphatase in the middle or late phase, and on the activity of β-glucosidase the early, middle or late phases.【Conclusion】The allelopathic substances released by the understory medicinal plants through rain or other ways, may affect decomposition of forest litter, nutrient release, soil enzyme activity, which hinders the maintenance of soil fertility and material recycling in the ecosystem and affects stability of the ecosystem. Therefore, it is suggested that T. mongolicum, M. haplocalyx and H. cordata should not be planted as understory in P. purdomii forests, or interplanting density of these plants should be kept lower to reduce the allelopathic effects.