Based on an analysis of the relationship between the signal-to-noise ratio and the threshold of timing synchronization，an optimal threshold curve of timing synchronization is fitted，and an adaptive threshold selection method of timing synchronization is proposed.The method applicable to all data-aided timing synchronization systems is applied to the lower-voltage orthogonal frequency division multiplexing（OFDM）power line carrier communication system to resist the harsh channel situation of power line and improve the timing synchronization performance.Simulation results show that the method outperforms the local relevant algorithm of fixed threshold with its frame error detection probability close to the optimal threshold curve.With its2dB function improvement than the fixed threshold method，this method is suitable for a power line communication environment with a low signal-to-noise ratio.