Network parameter errors may seriously restrict the online and offline application of the energy management system（EMS）. Based on the practical conditions of the electricity transmission network， the respective estimating equations of line reactance and shunt capacitance parameters are deducedderived respectively. Introducing the concepts of tree branches of a tree， links and minimum cycle basis groups of graph theory into the reactance parameter estimation， parameter estimations for the single case and multi-cases by supervisory control and data acquisition（SCADA） as well as for minimum cycle basis groups combining phase measurement unit（PMU） are derivededucedd. With the increasing of the quantity and category of the measurements， the observability analysis is implemented. Observability analysis is carried out according to number and kind increasing of measurements. The presented method has low requirements for PMU configuration and is tested on the New England 39-bus system in which four buses are equipped with PMUs. The parameter estimation results are good.