Abstract: Frequency offset synchronization is one of key apartment for orthogonal frequency division multiplexing system. A novel frequency offset estimation algorithm was proposed in this paper. It is based on null subcarriers distributed as Pseudo Noise (PN) sequences and overcomes the error induced by the channel frequency response zeros in traditional null-subcarriers methods. This method makes great use of good correlation properties of PN sequences. Integer offset estimation is achieved by position sequence cross-correlation calculation; meanwhile fraction offset estimation computation implemented by iterative steepest descent algorithm. Cost function calculated by this method will not produce more than the minimum, not the whole frequency domain search, dramatically reducing the amount of computation. According to the simulation results, this method improved estimation accuracy compared with maximum likelihood estimation algorithms based on cycle prefix, to verify its validity.