Terpenoids which widely exists in the higher plants is one of the metabolite of plants, and it plays a important role in the ecological systems. The relationship between the allelopathic effects and the community succession was reviewed. In this paper some subjects such as the bio synthesis of terpenoids, main plant species containing terpenoids, major compounds of terpenoids, ways of the terpenoids entering into environment and their water solubility were discussed. It was also expounded that the terpenoids can cause inhibition, promotion and autotoxic action on seed germination and seedling growth. The factors affacting these effects were also discussed.