There are problems of large loss, poor voltage quality and low annual return on investment of loss reduction equipment in 10 kV long distribution lines. Thus a double-layer iterative loss reduction and efficiency enhancement method for distribution lines combined with butterfly optimization is proposed. First, considering the three-phase imbalance of line load, the power system simulation software OpenDSS is used to establish a simulation model of the target distribution line. Second, the capacity and position of the reactive power compensation device of the 10 kV line and the position of the voltage regulator tap are added as the control variables, and the outer planning model with the maximum annual return on investment considering the life cycle cost (LCC) is established. The multi-objective model with the minimum annual active loss and annual average voltage offset is the inner operation model. Then using the butterfly algorithm to call the OpenDSS power flow calculation model simulation through Python, the power flow results and theoretical line losses are obtained and the loss reduction model is solved. Finally, the line of a power supply company is taken as an example for verification. The results show that this method can provide a practical implementation scheme for line loss reduction.