At present, there are more and more universities set up English-only instruction. As a new teaching reform attempt, English-only instruction plays an important role in cultivating internationally competitive high-quality talents, and promoting the construction of world-class university and world-class discipline in China. This paper mainly discussed English-only instruction which had been implemented in Chinese universities theoretically. It firstly summarized the connotation of English-only instruction, and then combed and compared related concepts. At the same time, it analyzed the reasons why universities implemented English-only instruction from the aspects of state, society and universities, and discussed the purposes of English-only instruction. At last, this paper pointed out the problems that should be paid attention to in the teaching process.