The invention relates to a built-in high voltage side electronic current transformer and a circuit breaker. The built-in high voltage electronic current transformer, which comprises high voltage side coaxially stacked Rogowski coil and low power coil; and the two coils are connected with a signal processing circuit. The built-in high voltage electronic current transformer is characterized in that: an energy taking coil is coaxial with the two coils, and the output of the energy taking coil is connected with a power circuit for supplying power to the signal processing circuit. The energy taking coil is arranged, the signal processing circuit and a power supply thereof are integrally arranged on the high voltage side of the transformer, and the power is directly taken from a bus, so that resources are saved, the operation is convenient to implement and the application is safe. For the circuit breaker with the built-in transformer and the electronic current transformer, the processing circuit and the power supply thereof are integrally arranged on the high voltage side, the energy is convenient to take, and the coils are suspended to prevent breakdown.