Both ginseng and American ginseng can not be replanted on the same soil consecutively. The article reviews the development and progress of studies on the replant failure of ginseng and American ginseng with a special focus on allelopathy in recent years. The allelopathy effect in ginseng and American ginseng is reviewed from following aspects: collecting and extracting allelochemicals, effects of such allelochemicals on seeds germination, seedlings growth, antioxidant enzyme activities in ginseng roots, growth of ginseng pathogens and ginseng callus, and more. It is presumed that inhibitory allelopathy is one of the many possible factors contributing to the replant failure of ginseng and American ginseng. Based on that, the paper points out problems in current researches on the allelopathic effect of ginseng and American ginseng: the allelochemicals are consist of a mixture, which one plays the specific role is not clear; concentrating on a single allelochemical while ignoring the interaction among allelochemicals. It is suggested that further study for this area should be focused on the interactions among allelochemicals and interactions between allelochemicals and environmental impact factors. Another area of needed research is that of the migration and transformation of allelochemicals in soil and microbial involvement in allelopathy on the growth of ginseng and American ginseng.