Abstract: In order to study the influence of DC bias on the transformer,a transformer modeling method under DC bias is proposed.The dynamic core magnetization curves method is built based on the JA theory.Then the transformer equation which formed by self and mutual inductance based on UMEC magnetic circuit model is deduced from the electromagnetic relationship,by combination of which the transformer simulation model under DC bias conditions is built.The model is used to analyze the core magnetization characteristics,the excitation currents and the harmonic changes of no-load transformer under different DC bias conditions.The results show that the model can reflect the hysteresis characteristics of the transformer core and the nonlinearity of the permeability under DC bias,the core saturation and excitation current amplitude and waveform distortion are also simulated accurately,which provides an effective means to study the excitation characteristics of transformer under DC bias.