Non-suicidal self-injury (NSSI) is a major global public health concern, defined as deliberate harm to one's own body tissue without suicidal intent. Drawing on the emotion regulation process model, which conceptualizes emotion regulation as the interaction of physiological, behavioral, and cognitive processes that alter emotional states, this study examines how stress, anxiety, and emotion regulation ability interact to sustain NSSI. A sample of 11,115 fifth- and sixth-grade students in Beijing (54.1% female; M age = 10.95, SD = 0.60) who had engaged in at least one episode of self-injury participated in four annual waves of data collection. Random-intercept cross-lagged panel models revealed that: (1) stress served as a negative trigger within the emotional system, showing an early negative association with NSSI but increasing later anxiety and NSSI severity; (2) NSSI and anxiety reinforced each other in a bidirectional vicious cycle, with each positively predicting the other over time; and (3) escalating NSSI impaired emotion regulation ability, which otherwise protected against anxiety. These findings suggest that worsening anxiety, stress, and the self-reinforcing nature of NSSI jointly deteriorate both the subjective-experiential system and the behavioral-expressive system, progressively undermining overall emotion regulation capacity. Early adolescent NSSI thus exhibits self-perpetuating characteristics, highlighting the importance of strengthening emotion regulation skills during high-risk periods to prevent onset and escalation. This study extends the benefit-impairment model by emphasizing both the preventive value of stress reduction and the role of early emotional changes in the development and maintenance of adolescent NSSI.