In this paper, a new symbol timing detection scheme robust to carrier frequency offset is proposed for Time Domain Synchronous (TDS) OFDM systems. The proposed method computes the sliding correlation from both the differential received signal and the differential PN sequence. Rapid symbol timing detection can be obtained based on the correlation peaks. As differential operation is adopted before sliding correlation in the proposed method, the time-dependent linear phase effect caused by the carrier frequency offset will not influence the correlation peaks. Nevertheless, the incorrect correlation peaks caused by the cross terms of the multipath may be detected. An ambiguity protection module is added to validate the correlation peak detection results and further improve the system performance. Our simulation results show that the proposed scheme for symbol timing detection is accurate and simultaneously robust to carrier frequency offset for TDS-OFDM systems in both a time-varying TU6 channel and a fixed two-path channel.