The invention provides a method and a system for realizing longest prefix match. The method comprises the following steps: partitioning a destination IP route needing writing of an installing route into two parts according to the storage capacity of a chip storage space; writing a first writing part into a TCAM (Ternary Content Addressable Memory); finding a Bitmap property table according to a second writing part, and setting a corresponding flag bit from 0 to 1; polling the Bitmap property table from a lowest order to a highest order, ranking flag bits which are set as 1 in sequence once again, and representing the flag bits with offset0, offset1, ......offsetx, wherein x is a positive integer, and is less than or equal to a numerical value corresponding to a top bit in the Bitmap property table; acquiring a Base_ptr base address of the TCAM storage corresponding to a current destination IP route and a ranking number of the offset bit in the Bitmap property table; and writing the second writing part of the current IP route into the SRAM (Static Random-Access Memory) oriented to the Base_ptr one by one according to the ranking sequence of the offset bits in the Bitmap property table. Through adoption of the method and the system for realizing longest prefix match, the utilization rate of the SRAM can be up to 100 percent.