“Letters of the Vietnam War” is a collection of letters from soldiers on the battlefield, recorded many stories during the bloody war years of the nation’s history, and it is a precious historical document about Vietnam’s war. Therefore, “Vietnam War Letters” are valuable for history education, used in history teaching as a source of source material to demonstrate, concretize, and contribute, authentically reproducing history. By means of theoretical research, content survey, synthesis, statistics, analysis, and comparison, we clarify the value of the collection “Letters of the Vietnam War” for teaching history and proposing methods to use those letters in teaching history in high schools through specific examples in lessons 16 - 17 of the History - Geography program 9 (Knowledge Connection set). The research results serve as a specific guide for teachers to apply when teaching this lesson and can research and exploit the use of “Vietnam War Letters” in other lessons at all levels, other educational activities.