From three dimensions of cultural dimension theory, namely Power Distance, Individualism vs. Collectivism and Long-term vs. Short-term Orientation, this paper aims to explore the differences in cross-cultural business communication between China and the U.S. mainly through case study, taking 1,357 English business emails as the research subjects. The results show that: (1) Under the perspective of Power Distance, Sino-US differences are mainly seen in decision-making. In Chinese companies, subordinates tend to obey the instructions and follow the suggestions of their superiors, while US companies are more lenient in decision making; (2) Sino-US differences under the Individualism vs. Collectivism dimension can be divided into two: value orientation of needs and speaking style, where the frequency of the value orientation of needs is reflected 70 times, while that of the speaking style is 57 times; (3) Under the dimension of Long-term vs. Short-term Orientation, Sino-US differences in terms of long-term and short-term interests are reflected in the reward of collaboration, usage rights of social posts and duration of collaboration. In general, the Chinese tends to pursue long-term interests, while the U.S. side is more concerned about the short-term interests. It is hoped that this paper will be helpful in guiding cross-cultural communication using business emails, and provide some reference for the future research on Sino-US differences in cross-cultural business communication and exchange.