In order to solve line loss calculation with incomplete measures and non-synchronous problem in distribution network, this paper presents a new solution. In terms of the monitoring data sources, load nodes are divided into three categories as the measurement nodes, power nodes and capacity nodes. The way of injection current calculation for electricity and capacity nodes are presented in detail, by this way, complete approximate real-time data will be obtained, and then flow algorithm of backward/forward sweep method is used to calculate line loss in distribution network. The solution due to considered the problem of synchronism, can avoid the calculation error of unsynchronism. Line loss calculation with this solution can provide the foundation for the operation and management decision in distribution network. Example shows that the solution is feasible.