The active ingredients of medicinal plants are the material basis of their clinical curative effects. They are also important indicators for evaluating the quality of medicinal materials. The synthesis and distribution of these active components show specific patterns depending on the genus, organ, tissue and growth period of the medicinal plant. Elucidating the dynamic accumulation and formation mechanisms of the active components in medicinal plants bears guiding significance for the quality control of medicinal materials and the improvement of clinical curative effects of traditional Chinese medicine (TCM). In this review, we have summarized recent progresses regarding how different growth stages affect the synthesis and accumulation of effective components in different parts (root, stem, leaf, flower, fruit and seed) of medicinal plants. We also provide an outlook on the research methods applied for the synthesis and accumulation mechanisms of secondary metabolites in medicinal plants. This study provides a theoretical basis for the regulation of secondary substance synthesis in production practices, the rational utilization of medicinal plants and the quality improvement of Chinese medicinal herbs.