A searching method is applicable to Gigabit-capable Passive Optical Network (GPON). The searching method includes: dividing a GPON Encapsulation Mode Port Identifier (GEM Port ID) of a GEM frame into a first portion GEM Port ID and a second portion GEM Port ID; performing a row look-up in a first memory array by using the first portion GEM Port ID, and performing a column look-up in the first memory array by using the second portion GEM Port ID; and identifying a specific bit's position in the first memory array, according to results of the row look-up and the column look-up in the first memory array, wherein the specific bit's position represents a GPON Encapsulation Mode Port (GEM Port) that is used by the GEM frame.