the present invention relates to a method of reducing complexity in a decoder which uses trellis decoding that can easily reduce the complexity of the decoder as much as required by reducing the paths itself using the statistics of path metric values and the reliability of the received signal . the method comprises first step of determining the reliability of bits received at the current level after initializing the level of the trellis and a flag , second step of determining the paths to be taken into account according to the reliability of received bits and computing and storing information about the determined paths and third step of obtaining the statistics of path metric values and a reference path metric by utilizing the determined path information at the current level , reducing the number of paths , and moving to the next level when total number of paths is larger than the number of maximum paths to be maintained .