The invention discloses a method for preparing a porous ceramsite filter material by using lepidolite extracted lithium slag. The lithium slag extracted by a lepidolite sodium chloride pressure digestion method is used as a main raw material. The method comprises the following steps of: adding partial ground clay powder serving as a plasticizer, adulterating a little amount of pore forming agent (one or two of carbon powder, bran powder, calcium carbonate powder and waste glass powder), balling, sintering and sintering. The filter material has the characteristics of low stacking density, highporosity, uniform pore distribution, high cylinder pressure strength and long service life. The method can simplify the production process and reduce the production cost, is favorable for pollution-free production of a lepidolite mineral lithium extracting process, and has significance for resource recycle and environmental friendliness.