The present invention discloses a symmetric double cascade DC conversion unit with circulating current reverse self-elimination capability. The unit can be used for DC voltage interconnection of different voltage levels under the condition of high voltage and high power. The DC conversion unit comprises two cascade modules, wherein input ends of the two cascade modules are in series connection, and output ends of the two cascade modules are also in series connection. Each cascade module consists of two modular multilevel converter (MMC) structures and an intermediate frequency transformer. The DC conversion unit is subjected to series-parallel modular combination to obtain a high voltage and high power DC converter, and finally the object of DC voltage conversion is realized. According to the unit, energy is transmitted dispersedly and the application of the single intermediate frequency transformer that may become the bottleneck of system application in a high voltage and large capacity situation is avoided, so that the unit has the advantages that the intermediate frequency transformer is easier to wind as compared with a conventional MMC type DC converter. According to the unit, a symmetric double cascade structure is used, so that the circulating current generated by the two MMCs in each cascade module is reversely self-eliminated via control; and DC conversion of more wide transformation ratio is realized by using a structure of the MMCs combined with series-parallel modular combination.