The invention discloses a preprocessed conjugate gradient method of converter transformer magnetic field analysis, which comprises the steps of (1) obtaining of converter transformer model parameters and (2) the preprocessed conjugate gradient determining method of the converter transformer magnetic field analysis, wherein the converter transformer model parameters comprise sizes of geometrical current converter transformer models and magnetic conductivity of each converter transformer element, and the preprocessed conjugate gradient determining method comprises steps of establishing and analyzing the models of the converter transformer magnetic field analysis, determining linear simultaneous equations of the converter transformer magnetic field analysis, determining unknown vectors of the converter transformer magnetic field by the preprocessed conjugate gradient method, and determining the distribution of converter transformer magnetic fields according to a solution of the converter transformer magnetic field analysis. The preprocessed conjugate gradient method of the converter transformer magnetic field analysis, which is disclosed by the invention, can determine the distribution of the current conversion changing magnetic fields so as to be used in the current conversion changing design and the fault analysis. Moreover, the preprocessed conjugate gradient method of the converter transformer magnetic field analysis can judge the sizes of a converter transformer magnetic field concentrating zone and average magnet density and magnetic leakage amplifying points, and can be used in design, operation and fault analysis of the converter transformer.