For Chinese doctoral students, English is the most essential subject when studying in U.S. universities and living life in the U.S. Using English not only promotes academic success, but also helps them to pursue better job opportunities and a better life in the U.S. The purpose of this study was to explore Chinese doctoral students' English use, perceptions of academic achievement in relation to their academic motivation and identity investment. Chinese doctoral student interviews, questionnaires, classroom observations, and journal entries were used in this qualitative case study. The findings of the study show that Chinese doctoral students' English use and perception of academic achievement had impacts on their academic motivation. Moreover, Chinese doctoral students' identities were also reflected in the investment of academic achievement.