Hadean is the oldest period of the Earth history, but it doesn’t get enough attention or recognition from the worldwide geologists due to the lack of reliable rock records. The term Hadean, which is used to define the period from the formation of the Earth to the appearance of the oldest rocks, was used in the suggested International Geological Time Scale in 2004AD. At present, the boundary of Hadean and Archaean is not definite. Geologists have different opinions on it (385Ga, 40Ga, 403Ga).Now, the Hadean rocks are discovered in two places of the world. One is Acasta, Canadia, where two tonalities and one metamorphic granodiorite were found. The zircon UPb ages of the former are 4002±4Ma and 4012±6Ma while the later is 4031±1Ma. Another place is Mount Sones, East Antarctia, where granulite faces tonalitic gneiss was found and its UPb age is 3927±10Ma. The oldest supracrustal rock(≥3870Ma) of the World was found in Greenland.In the antique Hadean, the rocks, formed in the earliest 600~700 Ma of the Earth history, experienced meteorite impact, crust recirculation and remelting, had disappeared mostly. At present, the Hadean is mainly recorded in the detrital or inherited zircons of the late rocks. >3800Ma detrital zircons have been found in more than ten areas in the world. The Jack Hills in Yilgarn Craton, western Australia, is the place which has the complete time spectrum of zircons. The ages of zircons in Jack hill are between 3800~4404Ma (most of them are between 3900~4200Ma) and the peak ages are 3840Ma, 3900~3920Ma, 4000~4200Ma, 4260~4300Ma, 4404Ma. Up to now, the accepted oldest detrital zircon age is 4404Ma. In addition, the Hadean detrital zircons are found in North America Craton, South Africa Craton, North China Craton and some young orogenic belts. These zircons are important media to study the Hadean geological events. According to studying on the Hadean detrital zircons, researchers raise many valuable questions that are worthy of further study. The first is the nature of the earliest crust. Some of the Hadean detrital zircons have compositional zoning similar to magmatic zircons after Archean, so the protolith of the detrital zircons are considered to be granitic rocks derived from remelting of the previous crust. Integrated analyses of the Hf isotopic characteristics of the detrital zircons indicate that they are derived from intermediate magma, so we can infer that the Hadean crust had intermediate composition. The genesis of the Hadean zircons is also an important subject. Basing on the study on content of Ti element in zircons, the crystallization temperature calculated through the Ti geothermometer and certain structural feature of zircons, some researchers insist that a large number of Hadean zircons are formed from the melting and crystallization caused by the meteoritic impact. Studying on the Hadean zircons is an important mean of retrospecting the impact events of the Earth. Diamonds and graphites are found in the 4300Ma detrital zircons. The diamonds indicate that the protolith experienced high pressure environment. The isotopic composition of graphite is similar to that of the organic carbon, so some researchers think it’s the sign of life. Some detrital zircons aged 4000Ma in several areas have a low Th/U ratio, which is the character of metamorphism, indicating the crust is considerable thick then. A number of important problems have been proposed by researching on Hadean detrital zircons. However, if we want to get credible and scientific understanding to the Hadean geology events and processes, more data should be obtained. So we should find more geological bodies and detrital zircons related to the Hadean, and strengthen the research on detrital zircons that have been found.