Studying the educational problems from the perspective of ecology, educational ecology has important implications in second language acquisition. Advocating people first and dynamic balance, ecological English classroom is one of the new progresses in the application of educational ecology to teach practice. There are many ways to build ecological English classroom. Based on such educational ecology theories as the law of tolerance and the optimum principle, the flowerpot effect and the law of

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... ducational ecology niche, this paper explores the application of code-switching in building ecological English classroom and arrives at the conclusion that code-switching has the following functions as the function to adapt to linguistic reality, the function to strengthen the language teaching effects, the function of affinity, the regulatory function, the function of implication and the support function.