A filter frame, a filter cartridge, and an assembling method of the filter cartridge are provided. The method has the following steps. A filter core and a filter frame are prepared. The filter frame has a glue-cutting segment. Glue is coated around an outer wall of the filter core, and then the filter frame, which is mounted around the filter core, is pushed toward the glue to make the glue-cutting segment press the glue until the glue is cut into two parts. The inner glue part disposed between the filter core and the filter frame seals the filter cartridge. The outer glue part is disposed on an outer side of the filter frame, and is superfluous and removed. The glue-coating is combined with the mounting of the filter frame, thereby saving time and effort.