Aiming at the problem that the calculation of the deterministic daily theoretical line loss rate of low-voltage distribution network is difficult to support the quantitative assessment of its fluctuation range, a probabilistic analysis method of the daily theoretical line loss rate of low-voltage distribution network is proposed. Firstly, consider the actual three-phase four-wire connection of the low-voltage distribution network, and assumes that the random models of three-phase voltage, distributed power output, three-phase active power and reactive power of the distribution transformer at the low-voltage side are known and simulated. Then, Source charge correlation is considered, and the latin hypercube sampling combining the equal probability transform principle with rank correlation is adopted. Finally, based on the Monte Carlo simulation method, the probabilistic distribution of the power flow and daily linear loss rate is calculated by the Newton injection current method considering the three-phase unbalance, which provides the decision basis for the low voltage distribution network loss reduction. The experimental data of Hengshan Garden in low-voltage distribution network prove the effectiveness of this method.