A high intensity discharge (HID) ballast circuit comprises a trigger circuit, a power half-bridge self-excited oscillation circuit, which is arranged to enable self-excited oscillation by energizing an angle capacitor Cgs with a Miller capacitor Cdg of a power MOSFET when an original single pulse output by the trigger circuit is excited, and then output self-excited oscillation signals; and a filter loop which is arranged to match impedance for the self-excited oscillation signals, thereby converting a low-impedance voltage source to a high-impedance constant current source. The inherent phase relationship of the power MOSFET is utilized, and oscillation signals are generated by a power half-bridge self-excited oscillation circuit, and then impedance matching for the oscillation signals is performed by the filter loop, and finally an HID lamp is triggered. As a result, damages to human eyes caused by stroboscopic effect can be avoided and electro magnetic compatibility test can be passed.