Objective: To test the effectiveness of psychological flexibility training on career adaptability among middle school students who undertook psychological courses based on acceptance commitment therapy and the adolescent mental flexibility model(DNA-V), and to provide a reference plan to improve the mental health of middle school students. Methods: This study recruited 110 junior high school students (60 boys and 50 girls) from a middle-school in Beijing. The students were randomly divided by class into a DNA-V face-to-face course group(offline group n=33), a DNA-V online course group(online group n=40), and a regular school psychology course group(control group n=37). Louise Hayes DNA-V intervention program was condensed into a six-hour middle-school DNA-V psychology curriculum. Using the Avoidance and Fusion Questionnaire for Youth and the Career Adaptability Scale, changes in psychological flexibility and career adaptability were measured before(T1), one week after(T2), and two months after (T3) the intervention. Results: Linear mixed models were used for the analysis, while controlling for demographic variables. Psychological flexibility and career adaptability in the offline group were higher at T2 and T3 than at T1(psychological flexibility t=4.22, 3.11; career adaptablity t=3.05, 4.16, P<0.01), while the difference between T2 and T3 was not statistically significant. The psychological flexibility and career adaptability of the online group were not statistically significant at T1, T2, and T3. The psychological flexibility and career adaptability of the control group increased from T1 to T2(t=4.64, 2.47, P<0.05), but T3 decreased back to a level close to T1. Conclusion In terms of both psychological flexibility and career adaptability, the DNA-V face-to-face psychology course resulted in a retention period of at least two months.