The current study tested the effects of an intervention based on the trans-contextual model (TCM) on secondary school PE students' sport injury prevention behavior and on theory-based motivational and social cognition mediators. Participants were PE students (N = 1168; Mage = 13.322 ± 1.045, range = 12-16; female = 51.721%) who participated in a 3-month cluster-randomized controlled trial. Schools were randomly assigned to a treatment group, in which PE teachers received training to be more supportive of psychological needs in teaching sport injury prevention, or a control group, in which PE teachers received no training. Participants completed survey measures of TCM variables and self-reported sport injury prevention behavior at baseline and at 3-month post-intervention follow-up. The proposed TCM model exhibited adequate fit with the data, χ2 = 143.080 (df = 19), CFI = 0.956, TLI = 0.916, RMSEA = 0.078 (90% CI = 0.066-0.090), and SRMR = 0.058. We found positive, statistically significant direct intervention effects on changes in perceived psychological need support (β = 0.064, p = 0.020). We also found positive, significant direct (β = 0.086-0.599, p < 0.001) and indirect (β = 0.002-0.027, p = 0.020-0.032) intervention effects on changes in TCM variables and behaviors to prevent sport injuries. Our findings support the TCM as a useful framework for building an intervention for promoting sport injury prevention behaviors among secondary school students.