To obtain the impedance parameters of distribution line accurately, a method for on-line virtual measurement of impedance for distribution line is proposed. According to three-phase current and voltage information collected from the head and end of the line, a linear equivalent calculative model of voltage drop is built. Then by use of mathematical methods, such as regression analysis method and solving equation groups utilizing average value, the method analyzes and calculates the coefficients of the voltage drop linear equivalent calculative model. The coefficient corresponding to terminal current is the impedance of the line. This is the calculation process of the parameters of the distribution line. The method is used to calculate the impedance of a running distribution line, and the calculation results and the actual impedance are compared and analyzed. The analysis results show that the on-line virtual measurement of impedance based on the voltage drop linear equivalent calculative model is feasible and effective, and this method has the advantages of fast computation and good real-time performance.