The system of this invention for extending address on UTOPIA and the method thereof can extend the single PHY on the ATM switching chip bus to many PHY ports easily without increasing too much cost, and thus increase the application flexibility of corresponding ATM switching chips. Evidently, there would be still many other embodiments of the invention, the people skilled in the art can make a variety of corresponding changes and transformations in accordance with the invention without departing from its spirit and essential, but these corresponding changes and transformations should also be in the protection range of the claims of this invention.