The invention provides a constant current source device for circuit breaker test. The constant current source device includes a current generator and an online feed forward compensation controller; the current generator is connected to an alternating voltage source and a circuit breaker, and includes a rectifier bridge circuit, a full bridge inversion circuit, an LCR filter circuit and a transformer which are successively connected; the online feed forward compensation controller is connected to the current generator, and includes a voltage transformer, a current transformer, an impedance online recognition and feed forward compensation control unit, and a PWM modulation drive unit, wherein the impedance online recognition and feed forward compensation control unit is connected to a primary coil of the transformer through the voltage transformer, is connected to a secondary coil of the transformer through the current transformer, and is connected to grids of each MOS transistor in the full bridge inversion circuit through the PWM modulation drive unit. Current guide waves can be avoided, the checking time is effectively shortened, the test efficiency is effectively improved, and the precision of test current can be ensured.