It is a time-consuming task to manually edit the power grid one-line diagram in an EMS. An automatic diagram generating method is proposed. The automatic diagram generation problem can be divided into two sub-problems: the substation placement and transmission lines layout. The gravitation-repulsion method is used to optimize substation placement. This method can efficiently calculate a good scheme. Based on this initial scheme， a genetic algorithm is also used to revise the solution. To solve the transmission lines layout problem， the labyrinth exploration method is used to make the lines connecting two substations straight and even. The software developed based on the proposed method has been embedded in a commercial grade EMS and proved practical.