A new model for the design of the city gas distribution network has been presented. On the basis of mass flow rates and pressure balances a nonlinear system of equation is obtained. A method for solving the latter is outlined which gives accurate results. Also, this method, when compared to the other accessible ones, takes less computer time. Finally in this method the actual length of network and pipe diameter can be considered. This is in contrast to the other methods in which certain quantities called "equivalent length" for different pipe size should be used.