To investigate whether growth mindset training can weaken the effect of math-gender stereotype threat on girl students, this study undertook experimental intervention in a group of grade-11 girl students and found that: (1) Mindsets can moderate the effect of math-gender stereotype threat. Girls with a growth mindset are less likely to be affected by math-gender stereotype threat compared with those with a fixed mindset. (2) Growth mindset training for girls with a fixed mindset can effectively reduce the effect of math-gender stereotype threat on their math performance.