An air filtering system includes a main system and a filtering module. The main system includes a main body having an air inlet, an air flow cover having an air outlet, and a primary filtering core replaceably disposed in the main body, wherein the air flow cover is detachably coupled at the main body to form a basic air filtering mode for filtering air from the air inlet to the air outlet through the primary filtering core. The filtering module is detachably coupled between the main body and the air flow cover to form an advanced air filtering mode, wherein the filtering module includes a secondary filtering core arranged for filtering the air after passing through the primary filtering core and before existing the air outlet.