To sovle the problem of Non-Data-Aided (NDA) sampling frequency synchronization for orthogonal frequency division multiplex (OFDM) systems, the CRB(Cramér-Rao Bound) of NDA sampling frequency synchronization algorithm was proposed. At first, the Probability Distribution Function (PDF) of received signal was deduced. Then, the CRB of NDA sampling frequency synchronization for OFDM systems was deduced according to its definition. At last, the CRB of NDA sampling frequency synchronization for OFDM systems in different modulation, sampling frequency offset and subcarrier number was presented.