There are three kinds of the electronic measurement transformer that apply in intelligent substation: optoelectronic transformer、active electronic current transformer and weak-mode small-signal transformer. As the key equipment of digitized substation process layer, how to select the electronic transformer is the practical problem confronted in intelligent substation construction. Through the introduction of the electronic transformers manufacturers, and the investigation of the digital substation in operation, the application situation of the electric transformer are analyzed and summarized. It also compares and analyzes these transformers from many aspects such as implementation principle, reliability and economy. At last the valuable idea for reference on selection is presented.