The present invention provides a method and an apparatus for determining a frame boundary of an FEC frame, and a decoding system, which are mainly applicable to an RS code and a BCH code. The method includes: receiving data, where the data includes N+P consecutive symbols with a first symbol being a starting point, N consecutive symbols with the first symbol being a starting point that are in the N+P consecutive symbols constitute a first data block, and N consecutive symbols with a second symbol being a starting point that are in the N+P consecutive symbols constitute a second data block; obtaining s parameter values corresponding to the first data block; determining a first iterative item and a second iterative item of the second data block; determining, according to the s parameter values corresponding to the first data block and the first iterative item and the second iterative item of the second data block, s parameter values corresponding to the second data block; and determining, according to the s parameter values corresponding to the second data block, whether the second symbol is a frame boundary of an FEC frame. The method for determining a frame boundary of an FEC frame disclosed in the present invention can improve efficiency of detecting a frame boundary of an FEC frame.