Abstract: An operational cost equation of a primary network in a district heating system is set up,taking the supply water temperature and the water flux as variables.The optimization objective of the equation is to minimize the operational cost,and its constraints are operational characteristics of the primary network.Based on the nonlinear programming theory,a constraint problem is then translated into an unconstrained one through the general constrained multiplier method,the conjugate gradient and linear search method are integrated together to solve the optimization problem,and the corresponding software program is also developed.Finally,the presented method and the step-by-step method are separately applied to a real urban district heating system.Result shows that the former is more effective and accurate than the later;the energy saving effect of quality-quantity regulation guided by the presented method is compared with the one of quality regulation,the former is proved to be prior to the later.