In this paper, we calculated balance-unbalance conversion factor, common mode current and leaked electric field in the power line with branch in high frequency by using the method of moments. A power line in general domestic has diverged variously. Especially, we paid attention to the lamp switch branch, in which only one line of the pair line is lengthened to make an ON/OFF switch. Furthermore, in order to improve the calculation accuracy, we measured lamp switch equivalent circuit for MHz band by the impedance analyzer. In order to confirm the validity of the calculation, we measured these characteristics of the same model beforehand, and compared the measurement value with the calculation value. As the result, the calculation and measurement values are approximated well in these characteristics. And the characteristics of power line with lamp switch branch in the condition of switch on and off are cleared up by these calculation and measurement.