This research discusses the medium and long term load forecasting techniques that are an essential basis for planning of such a distribution network taking into account the high penetration of DGs into network. The net load demand of HV/MV network has become more complicated, load forecasting encounters greater challenges than ever. Volatility and intermittency of DG sources such as wind and solar power greatly influences the load characteristics. A modern medium and long term load forecasting method for distribution network with DGs is investigated in this paper, which concerns time-varying characteristic of DG output power. The conventional spatial load forecasting results are collected, then the yearly time-varying curves of DG output using Monte Carlo simulation and the superposing time-varying curves of conventional load as well as DGs. From these the net-load forecasting result for distribution network is got, which is more accurate than ever.