Based on GPS technology and integral equations, a new method of live line measurement of the parameters of transmission lines with mutual inductance are proposed. The principle and mathematical model of the new method are explained in details. Data processing algorithm by least square method is introduced in the measurement. In order to take into account the influence of distributed capacitance of transmission lines, a modified mathematical model is introduced. Finally, an example of live line measuring two 220 kV transmission lines with mutual inductances in Central China grid is given. Comparison of results between the integral equations method and the conventional method is also shown. The field measurement results prove that the new method can meet the needs of live line measurement of transmission lines' parameters.