笔者于2019年夏季在哈佛大学霍顿图书馆发现1920—1923年间洪深与其导师贝克教授之间往来书信八封、贝克写给某编辑而涉及洪深的书信一封。这些书信绝大部分未曾被人提及，个别被提及的也还需要进一步研究。一百年前的这些书信对于洪深研究弥足珍贵，笔者特将它们译成中文，并试作初步考释。这些书信不但可以透露洪深早期在美国学习戏剧的经历、他的探索与思考，亦可以帮助学者重建洪深在美国戏剧圈里的人脉和关系。事实证明，洪深对于美国20世纪20年代的百老汇戏剧中心并不是外来者，而是一位直接参与者。信中提到的导演、演员来自美国甚至世界各地，他们将世界文化投射到戏剧舞台，也视戏剧为世界的舞台。在如此多样文化的影响之下，洪深的视野也是跨文化的。在哈佛大学和纽约的早期经历，对于洪深日后的戏剧生涯有着深刻的影响。

I did archival research at Harvard University in the summer of 2019 and found that there were eight letters between Hong Shen and his mentor, Professor George Pierce Baker, from 1920 to 1923. Moreover, a letter that Professor Baker wrote to a certain editor referred to Hong Shen. Most of these letters have never been mentioned in the literature, and those that were mentioned require further study. As these letters from a hundred years ago are valuable to research on Hong Shen, I have specially translated them into Chinese and have done a preliminary study. These letters not only reveal Hong Shen’s early experience of studying drama in the United States, his exploration and thinking expressed in these letters can also help scholars rebuild Hong Shen’s connections and relationships in the American drama circle. Facts uncovered in these letters have proven that Hong Shen was not an outsider to Broadway Theater in the 1920s in the United States, but rather an active and involved participant on the theater scene. The directors and actors mentioned in Hong Shen’s letters came not just from the United States but also from all over the world. They projected world culture onto the theater stage, and regarded theater as a world stage. Under the influence of such diverse cultures, Hong Shen’s vision was global and cross-cultural. Hong Shen’s early experiences at Harvard and New York had a profound impact on his future theater career in China.