In the absence of target language, English dictionaries serve as reference books, reference books and learning resources. It is not only conducive to increasing the amount of target language input for students, so as to achieve understandable input for students in the process of language learning, but also the use of English dictionaries in the process of language learning is the embodiment of second language vocabulary learning strategies and independent learning ability. Incidental vocabulary acquisition emphasizes the unintentional nature of vocabulary learning, and can also refer to the process in which the subject learns the corresponding vocabulary knowledge through input reinforcement without knowing the vocabulary test. The use of English learning dictionaries is not only conducive to the incidental acquisition of vocabulary knowledge, but also to the cultivation of learners' autonomous learning ability and vocabulary learning strategies. The use of English dictionaries is one of the vocabulary learning strategies. Through in-depth research on the use of English dictionaries, the learning strategies of second language vocabulary can be continuously improved and more effective vocabulary learning methods can be developed. At the same time, the use of English dictionaries involves related theories such as incidental acquisition theory, comprehensible input, input volume hypothesis, attention theory and processing level theory. This paper can further confirm the guidance of these theories in vocabulary teaching, and also find out the shortcomings of the theories so as to constantly supplement and improve the existing research theories.