In the economic integration process, English has become an important key to get a good career. Understanding the importance of English, Vietnamese government has paid more and more attention to teaching and learning English at High Schools. The English textbooks give teachers a chance to teach all skills (Reading, Speaking, Writing, Listening), instead of focusing on grammar like before. Now, accurate pronunciation is very important. This helps students communicate English better. As an English teacher with more than 10 years of experience at a high school, the author has found out that accurate pronunciation is basic but most of the students have problems in pronunciation. When teaching English for 10th grade students at Xuan Hoa High School, the author of this research realised that many students feel less confident in their speaking lessons for the reason of bad pronunciation. In order to improve the quality of teaching and learning English, the author investigated the common pronunciation mistakes by students and suggest some solutions to this problem. Firstly, The recordings were used to examine the existence of students’ mistakes in pronunciation. After that, the interviews were conducted to address the causes. A total of 130 tenth grade students at Xuan Hoa High School took part in the survey. From the answers of the students, the author stated that the tendency of students’ pronunciation mistakes were obvious. Based on the findings, the author proposed some strategies for teachers and students to improve the quality of teaching and learning pronunciation.