According to the literal meaning, the concept oflanguage teachercan be divided intolanguageandteacher. In the area of language teaching, the proficiency oflanguagehas been regarded as the only standard for teacher evaluation, so the traditional language teacher education and development, getting from thelanguageview put the emphasis on the unique characters of language teachers, and neglected the commonness ofteachers. This paper attempts to break the phenomenon that ESL teachers'development is controlled by the theories oflanguageandlinguistics, and from the perspective of constructivism, analyzes the issue of ESL teachers'professional development, for the establishment of subjectivity in ESL teachers'development and the implementation of independent and continuous development.Exordium illustrates the reason for title selection, the current research situation at home and abroad as well as the value and the train of thoughts in this dissertation.The first chapter makes an explanation upon the basic idea and teaching views of constructivism. It includes the basic meaning and theoretical origin of constructivism, the basic idea about the epistemology, learning and knowledge of constructivism, as well as its relevant pedagogy. The view about teaching and learning in constructivism established the subjectivity of learners, emphasizing the process of learning and development as the independent construction through social interaction, and the idea of social construction is the ideological basis for the whole dissertation.The second chapter mainly analyzes the concept ofESL Teachersunder the perspective of constructivism. Different from traditional idea, emphasizinglanguageandESL, the concept ofESL teachersis directed by the view of constructivism and its pedagogy, putting a survey on the roles of ESL teachers as subjectivity. This chapter illustrates the status of belief in the teaching practice for language teachers, the roles of ESL teachers under constructivism as well as the issue about evaluation.The third chapter, beginning with the cognizance of teachers'professional development under constructivism, illustrates the professional status of ESL teachers and the concept of ESL teachers'professional development. Following on, this chapter explains the meaning ofteachers'professional developmentunder constructivism, and through the comparison betweenteacher developmentunder constructivism andteacher trainingunder behaviorism, reveals the essence of ESL teachers'professional development. On the basis of the discussion above, this paper illustrates the contents and principles of ESL teachers' professional development. Under the perspective of constructivism, the contents of ESL teachers'professional development put the emphasis on the knowledge and consciousness for the realization of professional development, breaking the restriction of language proficiency. Moreover, this paper establishes teacher-center, teacher reflection and teacher cooperation as the basic principles for ESL teachers'professional development under constructivism, for the exertion of teachers'subjectivity.The chapters above put the emphasis particularly on theoretical illustration, but the fourth and the fifth chapters discuss the issue of ESL teachers'professional development from the practical perspective, emphasizing the importance of reflection as well as the practical approaches for ESL teachers'professional development. Reflection, reflective teaching practice and reflective model of teacher development establish the subjectivity of teachers, and are regarded as the key for the theory of professional development putting into practice. The practical approaches are the specific ways for the actualization of theory and the model of teachers'professional development.The sixth chapter mainly discusses the practice for the professional development of English language teachers. In China, English is regarded as a foreign language. From the language perspective, there exist differences between foreign language teachers and ESL teachers. However, the illustration in this paper is from the constructivism, so the difference between them two is less than their similarity. According to this kind of view, this chapter, combining with the theory and practice of ESL teachers'professional development, illustrates the practice of professional development for EFL teachers, in such three stages as pre-service, introductory and in-service development, promoting the quality and ability of English language teachers in China.