The invention relates to a method and platform for testing magnetic performance of a laminated iron core of a transformer in controllable excitation conditions. The method is related with a voltage regulator (1), a programmable frequency converter (2), an LC filter (5), a product-stage transformer laminated iron core model (6) and a power analyzer (9). A computer controls the programmable frequency converter to output needed pulse voltage uniform in amplitude but unequal in width, any needed voltage waveform is obtained after the pulse voltage is filtered, and the filtered waveform serves as excitation voltage of the product-stage transformer laminated iron core model for testing. If a PWM excitation condition needs to be produced, an LC filtering module is removed, and then an inverter directly supplies power to the laminated iron core model. The actual operation work conditions of the iron core of the transformer can be simulated, any voltage excitation condition such as harmonic wave under manual control, bias magnetism and PWM can be generated, and accordingly measurement of a laminated iron core magnetic field and loss performance can be measured in any given excitation condition.