The utility model discloses an all-in-one device for testing power frequency parameters and switching a test line for a high-voltage power transmission line. The device comprises a contactor KM1, a contactor KM2, a contactor KM3, a pilot frequency power supply, a potential transformer PT1, a potential transformer PT2, a potential transformer PT3, a current transformer CT1, a current transformer CT2, and a current transformer CT3. One end of an induction coil of the potential transformer PT1, one end of an induction coil of the potential transformer PT2 and one end of an induction coil of the potential transformer PT3 are respectively connected to the A, B and C phases of a three-phase power supply. The other end of the induction coil of the potential transformer PT1, the other end of the induction coil of the potential transformer PT2 and the other end of the induction coil of the potential transformer PT3 are respectively grounded. The current transformer CT1, the current transformer CT2 and the current transformer CT3 are respectively disposed on the A, B and C phases of the three-phase power supply. The output end of the potential transformer PT1, the output end of the potential transformer PT2, the output end of the potential transformer PT3, the output end of the current transformer CT1, the output end of the current transformer CT2 and the output end of the current transformer CT3 are respectively connected with the input end of a collection circuit. The output end of the collection circuit is connected with an upper computer. The device achieves the purposes of guaranteeing safety and automatic switching of a line.