In this paper, measurement and research of noise characterizations in three-phase four-wire low voltage power network channels are carried out. The power networks have overhead conductor structures. Measurement frequency is from 1kHz to 1MHz. The studies include noise classification and load characterizations, noise distribution characterization along the power lines and noise distribution characterization when coupling across different phases. The measurements of noise distribution characterizations are carried out simultaneously with two sets of instrument of the same performance, in order to eliminate the influence of time variance and improve measurement accuracy. The measurement results illustrate that at the interest frequencies, noises of power networks are mainly produced by the loads. The closer to the noise source (loads), the higher level the noise is. Noise level varies from different coupling phases. Noise level of phase to phase coupling is usually far less than or at least not greater than the noise level of the related two single phase to neutral coupling, respectively. At lower frequencies, the spectrum density level of the power-frequency harmonic noise is much higher than background noise.