1. An address learning method for a network device having a plurality of connection ports, at least one of which is electrically connected to a terminal device, the method comprising: a fetching process for fetching an address data string from a first memory unit by a programmable logic device; a hashed-address generating process for generating a hashed-address by the programmable logic device; a data registering process for writing the address data string into a data table; and an address registering process for writing the hashed-address into a hashed-address table, wherein the method is applied to a calculator program executed by a computing unit, wherein the computing unit reads the address data string and the hashed-address respectively from the data table and the hashed-address table and writes the address data string into an address of a third memory unit corresponding to the hashed-address, wherein the computing unit writes a deletion address into a deletion address table and outputs a deletion instruction to the programmable logic device, and wherein the programmable logic device fetches the deletion address from the deletion address table and deletes data in an address of the third memory unit corresponding to the deletion address.