Teaching Vietnamese to foreigners in the era of integration is extremely necessary. Currently, the team of Vietnamese language teachers and instructors across the country has been and is being given due attention by the Party and the State, enjoying very reasonable preferential policies. However, in the process of fulfilling this noble mission, volunteer workers spreading Vietnamese globally have inevitably made regrettable mistakes, causing Vietnamese learners to spend too much time studying without being able to speak and write Vietnamese properly. Consequently, they become discouraged and reluctant to learn Vietnamese. Given this situation, I will identify the reasons leading to intonation errors and propose necessary measures to rectify these mistakes, enabling teachers and colleagues to effectively accomplish their tasks as expected.