Abstract: There is a big difference between transmission line reactive power state estimation results and actual measured values, which seriously affects the normal operation of power grid analysis and other links.As a kind of static basic data, the accuracy of transmission line parameters affects the result of state estimation.In order to solve the low reactive power state estimation accuracy of the short-distance non-transposition double-circuit transmission line on the same tower with the power plant directly connected to the grid, through PSCAD simulate line connected to the grid operation, the line phase modeling is carried out, it proposed the method of line parameter correction, and then, the line parameters which can accurately reflect the running state of double-circuit line in the same tower was obtained.Finally, it analysde the influence of the self-inductance and mutual inductance of lines under different phase sequence arrangements and the reasons for low accuracy of line reactive power.