Academic literacy development is shaped by multiple individual and contextual factors that mutually interact with one another. Previous studies have identified some of the factors, but few explored their complex and dynamic interactions in students' writing practices. The study adopts a case study method to examine EFL learners' academic literacy development from an ecological perspective. Findings reveal that (1) affordances and constraints are not predetermined categories but are interactive and emergent; (2) personal traits largely shape the way learners perceive, appropriate, and interact with contextual affordances; (3) complex person-environment interactions are generally situated within the dialectical relationship between agency and structure in connected literate activities; (4) the way students characterize and shape their relations with contextual affordances/constraints bears developmental effects. The study unveils complex person-environment interactions in EFL learners' academic literacy development while shedding light on relevant pedagogical practices.