Firstly， combining the characteristics of middle voltage distribution network planning， a loss coefficient method for estimating the real power loss of a main feeder is introduced. Then it is expanded to estimate the voltage drop of a main feeder under various typical load distributions. The voltage drop coefficient table is also given， with which a fast identification of low voltage can be realized for a main feeder under different load distributions. In addition， the loss estimation of distribution transformers is considered in the loss coefficient method. This paper aims at providing practical reference for distribution network planning.