Corilagin is a naturally occurring water-soluble retrogallic acid tannin, which can be extracted from many kinds of plants. Known at present, it is the main effective ingredient of Phyllanthus urinaria L., Geranium wilfordii Maxim., Phyllanthus matsumurae Hayata, and Trifolium repens L. It also exists in Phyllanthus emblica L., Dimocarpus longan Lour., Canarium album (Lour.) Raeusch., and Terminalia chebula Retz. It can participate in a variety of signaling pathways in vivo and has multiple biological activities, including antitumor, anti-microbial, anti-oxidation, anti-inflammation, hepatoprotective, anti-allergy, anti-proliferation and so on. Given the limited efficacy of first-line treatments for many diseases such as oncology, chronic liver disease, and rheumatic immune system diseases, and the potential for adverse effects to outweigh the therapeutic effects, attention is being focused on alternative treatments, and natural plant extracts are a natural target for alternative treatments, as natural substances tend to have low toxicity to normal tissues. Some proprietary Chinese medicines containing corilagin have been used in clinical applications, being clinically applied to treat chronic liver disease, viral hepatitis B, rheumatoid arthritis and other diseases. This paper reviews the extraction, determination, distribution and harvesting, pharmacokinetics, biological activity, safety assessment of corilagin and its application in clinical practice.