Abstract:“Reserve, cover, tunnel, source” is a brief introduction of geothermal formation conditions. Depending on geothermal exploration in several years, it is regarded that “reserve, cover, tunnel, source” is a necessary conditon of geothermal formation, while deep “confined water” detention” is a full conditon of geothermal formation. “reserve, cover, tunnel, source, detention” is the sufficient and necessary conditions of geothermal formation.