Abstract: Line loss is an important indicator to measure emission reduction and operation efficiency of distribution systems. To achieve carbon peaking and carbon neutrality goals, a large number of stochastic and intermittent renewables are connected to the distribution network, which brings new challenges to the calculation of distribution network line loss. In this paper, from the perspective of probability, the distribution network line loss probability distribution expression is derived based on generalized non-central chi-square distribution and the Gaussian mixture model under arbitrary current distribution. On this basis, the expressions of mean, variance and moment generating functions of line loss are given, and a numerical expression of line loss probability density function and cumulative probability distribution function based on Raphaeli series is proposed. The case study on the IEEE 33 bus system verifies the high accuracy and efficiency of the proposed line loss probability distribution calculation method.