Combined with the construction of DSCADA (distribution SCADA), which is being implemented by SMEPC, a practical calculation method of theoretical line loss in 10 kV power distribution network based on DSCADA and power flow is put forward in this paper. Due to the fact that not all data can be acquired during the construction of DSCADA, the paper considers the customer information of distribution transformer and power consumption with the help of CIS and PMS synthetically to acquire the actual load data as far as possible. Especially, the designed algorithm also considers the installation position of CT which would influence the calculation result. In this paper, the flow of calculation process is presented. The relevant program based on distribution flow is also put forward to simulate the actual situation in distribution network and verify the algorithm. In this paper, an example is simulated to show that the designed algorithm is reasonable and valid.