With the development of advanced automation and information technologies, more intelligent meters and measurements are involved in the management of modern district heating systems. A huge amount of measured data can be exploited to technical improvements and environmental protections besides billing purpose. In this paper, a new model is proposed to estimate onsite heat losses of a general pipe network with hourly measurements of heat sources and substations. A detailed heat loss profile along each pipe can be obtained by the proposed model, which can significantly improve the accuracy of the location of damaged insulation. Furthermore, the thermal deterioration of buried pipes can also be evaluated conveniently. In the case study, a real district heating system which has 3 heat sources and 34 substations is analyzed to validate the proposed model. The onsite heat losses of all pipes for 24 h are calculated by the hourly measured data. The results indicate that the heat loss profile of a return pipe is lower and more fluctuating than that of corresponding supply one. The heat losses of selected pipes are nearly 3.51-8.32% more than the reference values, which indicate that selected pipes' insulations are of a little aging or corroded by surrounding soil.