A system for automatically sorting a mailpostal matter and a method thereof are provided. The system for automatically sorting a mailpostal matter includes a mailpostal matter supply unit configured to convey two inputted mailpostal matters by controlling a distance between the two inputted mailpostal matters to be equal to a distance between carriers when the two mailpostal matters are inputted through one inlet at the same time, a mailpostal matter inserting unit, configured to insert the two conveyed mailpostal matters into two crossbelt carriers which are continuously empty at the same time when the two mailpostal matters are conveyed from the mailpostal matter supply unit, and a crossbelt carrier configured to move the two mailpostal matters inserted from the mailpostal matter inserting unit.