The authors definitely make out the concept of loop main pipeline, supplying main pipeline and ramiform branch line, as well as the order of their hydraulic calculation. Then they puts forward the principia of how to study out the direction of loop main pipeline and presents the method of making flux initial distribution. The matrix of loop main pipeline hydraulic square dispersion is set up. The node referenced pressure is defined and the equation of how to calculate it is deduced. A software is developed to calculate the loop main pipeline hydraulic square dispersion. The method of calculating ramiform branch margin impetus is given.