The invention provides a filler matrix for treating landfill leachate, and a preparation method and an application thereof. The filler matrix makes a medium and a material fully mixed in the culture processing, and functional microorganisms are quickly attached to the surface of ceramsite in the culture process, go through a porous structure and enter the ceramsite, so the functional microorganisms are rapidly enriched, and the subsequent efficient removal of contaminants is benefited; and the ceramsite in the filler matrix can increase the skeleton structure of the matrix, so the sedimentation and compaction induced blocking phenomenon of a filter bed in the working process is effectively avoided, and the hydraulic shock resistance in the working process is significantly improved. The invention also provides the filter bed. The filter bed uses the filler matrix to effectively improve the blocking problem and effectively reduce COD and ammonia nitrogen in the leachate.