<p>Self-critical perfectionism represents a key vulnerability factor for adolescent non-suicidal self-injury (NSSI). Yet, given that most research relies on cross-sectional methods, little is known about the circumstances and processes through which this form of perfectionism is associated with NSSI. Drawing on self-determination theory, this one-year longitudinal study investigated a mediation pathway in which basic psychological need frustration linked self-critical perfectionism to NSSI and examined whether intentional self-regulation moderated this indirect pathway. Data collection occurred at three intervals (T1, T2, T3), each separated by six months. The final sample consisted of 1,258 Chinese adolescents (<i>M</i>_<i>age</i> at T1 = 13.78 years, <i>SD</i> = 1.41; 50.1% girls) who completed questionnaires assessing self-critical perfectionism, basic psychological needs frustration, intentional self-regulation, and NSSI. The results suggested that, after accounting for gender, age, and baseline levels of need frustration and NSSI, T2 need frustration served as a longitudinal mediator between T1 self-critical perfectionism and T3 NSSI. Furthermore, the link between T2 need frustration and T3 NSSI, representing the second stage of the mediation model, was moderated by T2 intentional self-regulation, such that greater intentional self-regulation among adolescents attenuated this association. These findings underscore adolescence as a key developmental stage where perfectionism, need frustration, and self-regulation interact to shape NSSI risk.</p>