The invention discloses a device and method for extracting humic acid from decomposed coal. The device comprises a pulverizer, a separator, an alkali reaction barrel, an acid reaction barrel, a circulating pump, a filter and a dryer. The pulverizer is sequentially connected with the separator, the alkali reaction barrel, the acid reaction barrel, the circulating pump and the dryer, the filter is communicated with the acid reaction barrel and the circulating pump, and a circulating loop is formed and used for pumping acidized humic-acid-containing materials into the filter for circulating concentration and adding water to the concentrated humic-acid-containing materials for circulating washing. By means of a rapid filtering mode of the filter, the washing process time is greatly shortened, the washing process can be completed within 2 hours, clarification washing equipment is greatly reduced, meanwhile, humic acid liquid can be highly concentrated, investment of humic acid drying equipment is reduced, and consumption of dry steam is greatly reduced.