The invention provides a double-circuit power supply circuit for a 50MW alternating current heater. The circuit includes two power supply circuit bodies and the alternating current arc heater, wherein the two power supply circuit bodies are same in structure and each includes a heater feed-out cabinet, a heater startup cabinet, an isolating switch, a choke reactor and a high-voltage measurement device. The heater feed-out cabinets are mainly used for feeding 10 KV of power of a 110 KV transformer station out to a 10 KV distribution room and is used for power supply line protection at the same time; each heater startup cabinet is a switch device which is large in power and high in breaking capacity, and is used for starting and stopping the operation of the corresponding alternating current arc heater, each isolating switch forms a visible breaking point when the alternating current arc heater and the choke reactor are maintained; each choke reactor is a hollow electric reactor with multiple grading reactor bodies, is used for regulating current of the corresponding alternating current arc heater, and plays a role in stabilizing the current; each high-voltage measurement device is used for measuring the voltage and current of an electric arc end; each alternating current arc heater is a device which generates electric arc by means of a high-voltage alternating current power supply.