Aiming at the accurate calculation of limit line loss of distribution network affected by large-scale new energy access, load correlation and system uncertain harmonics, a calculation model of distribution network limit line loss considering correlation and harmonic loss is constructed in this paper. Firstly, the semi-invariant model of DG and EV output is established. Secondly, the improved Nataf transform is used to deal with the correlation of load output, and the load semi-invariant model considering the correlation is established. Then, the variation of line and transformer losses with harmonic content is analyzed, and the corresponding correlation model is established by exponential fitting. The semi-invariants of the state variables are solved by the probabilistic power flow model, and the probability distribution of the state variables is fitted by the Cornish-Fisher, and then, the limit line loss of the distribution network is obtained. Finally, the IEEE 34-bus system with new energy is analyzed, and the calculation results verify the accuracy of the proposed model.