Abstract: Intermediate-frequency power supply is widely used in induction melting and heat treatment. It is difficult to start up with this kind of power supply on a heavier load. A double assistant-bridge starting circuit is brought forward, based on which a thyristor parallel inverter intermediate-frequency power supply is proposed for induction heating applications. The start-up of heavy load with a DC equivalent resistance of only 0.04Ω(corresponding to an AC equivalent impedance of 0.16Ω at low voltage, and an equivalent load of 45t with only 4-turns of induction coil is introduced). This technique overcomes the key difficulty in the realization of an intermediate-frequency induction furnace over 50t.