Polygonum capitatum (Polygonaceae) exists in rural areas of Southwest China and some other Asian countries. Its aerial part or whole herbal plant has been used as a Miao ethnomedicine against urinary system diseases, infections, pyelonephritis, diarrhea, and so on. The progress in phytochemical research on P. capitatum over the past decades is summarized. Two hundred and three chemical constituents that have been isolated and identified from this plant are included in this article, the chemical structures of which include aliphatic hydrocarbons, aliphatic alcohols, aliphatic ketones, aromatic aldehydes, aliphatic acids, glycerides, triterpenic acids, sterols, anthraquinones, chromones and their glycosides, flavonoids and their glycosides, phenols, phenolic acids and their esters, lignanoids, flavonolignans, phenolic glycosides, alcoholic glycosides, amino acids, nucleobases, amides, alkaloids, alkyl glycosides, volatile oils, and polysaccharides.