In order to estimate the equivalent parameters of the external network online when its external network information is insufficient, this paper proposes a method to real-timely identify the static equivalent parameters of multi-port external network using recursive least squares algorithm. This method utilizes the one-step state estimation of the internal network after blocking the external network, and obtains the actual measurements of optimized boundary information of the internal network branches without outage the branches. Based on the boundary information, the multi-port extended voltage source network model and the π-type equivalent branches are selected to model the external network respectively. The two-step recursive least square method with data correction function is adopted to identify the equivalent parameters of the external network. The simulation results of the IEEE30 system and Hunan 528-node system verify the accuracy of the algorithm and it can be applied to the static equivalence of the online external network. This work is supported by Research Fund for the Doctoral Program of Higher Education of China (No. 20110141110032).