Idioms are the essence of language culture, concise and comprehensive phrases or short sentences formed in the long term use of people. They are rich in national cultural characteristics. The purpose of this paper is to study Chinese English learners' understanding of English animal idioms. First of all, it introduces the characteristics of English idioms and the three problems that should be paid attention to in the translation of English idioms, and expounds the understanding of idioms and the translation of animal idioms. In this study, 60 English majors and 60 graduate students were chosen to investigate whether English proficiency affects their understanding of idioms. The experimental results show that the average scores of Senior English learners are 4.00, 2.73, 1.00 and 0.83, respectively. Among the four kinds of animal idioms, regardless of their English level, the average scores of class I, II, III and IV are 3.73, 2.52, 0.90 and 0.77 respectively. Among the four types of English Animal Idiom Comprehension, English learners' English proficiency affects the comprehension results of the first and second types of idioms. In type I, English proficiency has a significant effect on the understanding of animal idioms (t = -3.00; P = 0.004 < 0.05). That is to say, learners with high English proficiency perform better than those with low English proficiency in understanding animal idioms. In the second category, the influence of English level on the understanding of animal idioms is also significant (t = -2.33; P = 0.023 < 0.05).