This paper presents that D,yn11 is recommended as the connection mode of dis-tribution transformer in distribution system with three-phase unbalanced loads,and Y,yn0 is not inthe electric design standards modified in recent years.The performance comparison between D,yn11and Y,yn0 under the operating condition of no load,unbalanced load,single-phase short are made.The D,yn11 is better than Y,yn0.