The present study adopts a mixed method design to investigate the effect of seven classroom assessment (CA) features on student self-regulated learning (SRL) and further explored factors that influenced the effect. Twelve teachers and their students (valid data points tallying 630) from three Chinese high schools participated in the study. Structural equational modelling results showed that the CA features had varied impacts. Specifically, self-assessment most effectively enhanced SRL, followed by teacher instruction and structured guidance, then teacher feedback; assessment task and student choice had mixed impacts. Peer-assessment and CA environment reduced SRL. Five influencing factors were revealed through both teacher and student interviews, namely, student engagement with the assessment task, student dependence on authority, prospective gains in the gaokao, intractable motivation and learning approach, and student-teacher relationship. The research has practical implications for SRL promotion.