Abstract: With more and more construction of oversea hydropower stations undertaken by China, and due to the differences in standards, design and manufacture habits, the phase sequence and groups of Chinese made transformers are not complied with local requirement. To this case, it is urgent to solve the problems including whether the transformer can be put into system and what is the change of the connection and its corresponding effects, and how to change the transformer phase sequence of the manufactured product, etc. Combined with practical engineering, the relationship between phase sequence (change) and groups for large transformer, the comparison of sequence adjustment scheme, the method and principle are analyzed and discussed. The results show that the cost of the change of the terminal connecting of LV winding side is higher, but it can solve the problem completely and minimize the influence on the project and system.