A micro-grid contains quite a few distributed generators besides multiple loads. The power generated from these distributed generators may vary greatly over time. Therefore， the micro-grid may have different power generating or consuming characteristics in different time slots. First， a mathematical model for micro-grid power generating and consuming characteristics is developed. Then， a distribution network planning method containing a small proportion of micro-grids is studied， including the method of distribution substation planning， restrictions on micro-grid access to network， and the model of distribution network structure planning. Finally， a distribution network planning example is used to analyze and verify the planning method.