This paper presents a channel measurement method for low-voltage power networks. Firstly, the measurement parameters and tools for the channel transmission characteristic are introduced. Then the basic principles for measuring Low-voltage power line noise, signal transmission loss, power line impedance characteristics are introduced too. In the end, the measurement and the analysis results are given. Those results show that the environmental noise are large in the middle and low frequency bands large, the lines attenuate seriously when the frequency is 220kHz, as well as that the impedance characteristics is stable when the power frequency nearby zero in the high-frequency regions, from which we can conclude that the optimal transmission frequency is between 350kHz~450Khz. Besides, the noise is low and the impedance is stable when power frequency nearby zero-crossing, and it means that the low-voltage power grid presents high impedance and stable, low noise level, suitable for signal transmission, and to facilitate the system time synchronization.