Abstract: The failure rate of converter transformer is significantly higher than that of ordinary power transformers. Insulation aging under coupling of electromagnetic, thermal and fluid multi-physical fields is the primary reason for threatening their safe and reliable operation. Based on the electromagnetic field and temperature field of converter transformer, the coupling mechanism for complex structure of converter transformer is studied. The numerical calculation methods of electric field under AC/DC composite voltage and polarity reversal voltage, electric field counting ion migration model, magnetic field and loss considering non-sinusoidal current, and temperature field considering fluid-thermal coupling and electromagnetic-fluid-thermal coupling of converter transformer are summarized. The research trend of multi-physical field coupling is prospected. It is pointed out that the key direction of future research will focus on the influences of space and interface charges on the electric field distribution in oil-pressboard insulation systems of converter transformers, the influence of temperature field on the performance parameters of insulating materials, the influence of heat dissipation mode on temperature field, and the more comprehensive coupling and loss calculation of temperature field and fluid field. The summary of these research results can be used to realize the accurate quantification of the distribution of each physical field, which in turn provides reference for the previous design optimization and later efficient operation and maintenance of the converter transformer.