This paper introduces a novel post-processing algorithm for low-density parity-check (LDPC) codes adequate for NAND flash memory, to improve error correction capability of a soft decision decoding by reducing strong error effects in an efficient way. In this algorithm, it can detect variable nodes of strong errors using incoming check-to-variable (c2v) messages and reduce magnitude of channel reliability of the nodes to avoid supplying large erroneous variable-to-check (v2c) messages for the check nodes. The proposed post processing algorithm with a finite precision LDPC decoding scheme is named edge-based post processing and effectively reflects time varying characteristic of NAND flash channel.