The traditional distribution network planning method ignores of the power difference before and after the distributed generation is connected to the distribution network, which leads to a high construction cost. Therefore, a distribution network planning optimization method is proposed on the basis of the urban energy internet. Firstly, the power of the distributed generator is calculated before and after it is connected to the distribution network. And then, the load changes are compared in terms of the power change, so as to determine the influencing factors of the urban energy internet on the distribution network. Based on these influencing factors, a load forecasting model is established to predict the change of distribution network load under the influence of urban energy internet. Finally, the constraints are introduced for power supply and demand balance, power flow capacity, voltage and current, etc., and the distribution network planning optimization model is constructed successfully. An example is included for verification. It is shown that the regional load forecasting is precise, and the difference between the forecasted performance and the actual value is small. The proposed method can reduce the investment and operation cost of distribution network planning and construction to realize a reasonable distribution network planning.