With the minimum total cost of pipe network taken as the goal, the pipe diameter, the cold water flow rate and the thickness of the pipe insulation layer taken as the optimization variables, the user cooling load demand and the reasonable cold water flow velocity range taken as the constraint conditions, an effort has been made to establish the objective function of the pipe network optimization of the district cooling system, with the orthogonal optimization method adopted to optimize the calculation. The results show that: arranged in a descending order, the influence of design parameterson the economical efficiencyof the pipe network will be: d (pipe diameter), v (velocity), δt (thermal insulation layer thickness), with all the three factors being fundamentally indispensable; the optimal design parameters of the district cooling system in Zhuzhou Shennong Urban District will be: de = 300 mm, ve = 1.06 m/s, δte = 0.057 m, with its annual total cost being 282 729 yuan; the orthogonal optimization method, which can be used as an optimization tool for the optimal design of pipe network in the district cooling system, proves to be useful and helpful for the general engineers and technicians.