From the perspective of dynamic systems theory, the present study investigated the dynamic development of five college students’ English learning motivation over the course of two semesters, focusing on the characteristics of motivational trajectory, features of motivational state space and the co-adaptation of systems. The results show that： 1. the motivational development trajectories of the five students have both converged and deviated; there is no linear relationship between the initial conditions and the development trajectory of the motivation. And there are obvious individual differences in the motivational development of the five students, with three main patterns of “steady development to fluctuant development”, “steady rise” and “fluctuant development; 2 . there are mainly two attractors and two repellors in the state space of motivational development, with different kinds of English exams being the main cause of attractor basin; 3. the co-adaptation between system components includes the coadaptation between different subjects, different tasks of the same subject, as well as learner and environment. The study is helpful for teachers to learn about the complex dynamic characteristics of students’ English learning motivation so as to enhance their students’ motivation by adopting various motivating strategies.