The complex electromagnetic coupling between transmission lines exists in multi-circuit transmission line on the same tower. When the radial network forms loop network, the imbalance of each part of transmission lines will be superimposed, which will aggravate the problem of three-phase imbalance of loop network. In order to decrease the three-phase imbalance of transmission lines, this paper analyzes the relation between current and impedance of transmission lines in loop network under different phase sequence arrangements, and it also proposes that if each part of it applies the same phase sequence arrangement, the unbalanced degree of transmission lines in loop network can be greatly reduced. Through analyzing the model of loop network consists of double-circuit transmission lines by PSCAD/EMTDC, and comparing the unbalanced degree under different phase sequence arrangements, the results verify that if both of the transmission lines use the same phase sequence arrangement or inverse phase sequence arrangement, the imbalance degree of transmission lines is smaller, which provides theoretical basis to the optimal phase sequence arrangement of loop network.