This paper reports a longitudinal study on Chinese college EFL learners'English classroom engagement dynamics by adopting the high-density repeated measurement approach.An intact class of 31 students in a comprehensive university in central China participate in the semester-long study.It is found that within the 90 minutes of each class,the students show dy-namic fluctuations in terms of behavioral,cognitive and emotional engagement intensity.Overall,their engagement develop-ment can be classified into five types,namely,small-scale fluctuations,stably high level of engagement,large-scale fluctua-tions,stably low level of engagement,and stably medium level of engagement.For most of the students,despite the occasional variations of large-scale fluctuations or stably low/medium level of engagement due to the disturbance of external factors,a state of small-scale fluctuations or stably high level of engagement emerges along with their co-adaptations in the college Eng-lish class.A very small number of students have comparatively high-frequency variations of large-scale fluctuations or stably low/medium level of engagement,which might be attributed to their initial state of English learning(i.e.a very poor English foundation)or the ambiguous perception of English learning goals and English-learner identity construction at college.