Left‐behind children, as a large‐scale disadvantaged group, encounter an array of risk factors that impede their academic development because of parental migration. The current study aimed at investigating the roles of left‐behind cumulative risk and growth mindset on academic adjustment and exploring whether growth mindset moderated the association between left‐behind cumulative risk and academic adjustment in left‐behind middle school students. A total of 1184 left‐behind middle school students (615 males; 12–16 years) participated in the study. Results indicated that left‐behind cumulative risk is negatively associated with academic adjustment in middle school students (β = −.199, t(1183) = −7.229, p < .001). Besides, growth mindset has a protective effect on left‐behind middle school students' academic adjustment (β = .386, t(1183) = 14.070, p < .001) and a moderating effect on the relationship between left‐behind cumulative risk and academic adjustment (β = .394, t(1182) = 4.057, p < .001, ΔR2 = .012). These findings suggest that family risk factors related to left‐behind status affect the academic adjustment of left‐behind middle school students in a superposition way, while the positive individual factor of growth mindset could protect the negative impact caused by parental migration.