Abstract: Distribution network theoretical line loss calculation is an important technical measure for the management and analysis of distribution line loss. Aiming at the problems that the traditional distribution network theoretical line loss calculation can not be realized automatically, the workload is large, and the calculation result is inaccurate, etc., a theoretical line loss calculation method of distribution network based on integrated power and line loss management system is proposed. Taking the calculation of the distribution loss of the distribution network of Fujian Putian Power Supply Company as an example, the online loss calculation of distribution network theory is carried out and compared with the traditional theoretical line loss calculation results. The results show that the theoretical line loss calculation method of distribution network based on integrated power and line loss management system can achieve the same or even higher calculation accuracy as the traditional theoretical line loss calculation method. At the same time, it can improve the automation degree of current theoretical calculation of line loss, and reduce the line Loss of workload in theoretical calculations improves the efficiency of grid companies' distribution network operations..