Disclosed are an LDPC encoding/decoding method and a device using same. The method includes the steps of: (a) generating an information bit sequence by determining information bits to be encoded from among a group of information bits; (b) generating a modified information bit sequence by inserting a preset error floor prevention bit into at least one preset position in the information bit sequence; (c) generating a parity check bit on the basis of the modified information bit sequence; and (d) performing encoding by using the modified information bit sequence and the parity check bit. According to the disclosed method, performance degradation of LDPC encoding and decoding due to an error floor phenomenon can be prevented.