Although gender stereotypes in the STEM fields have been robustly studied, the research targets have rarely included international high school students in China. This study aims to explore how gender stereotypes influence Chinese international high school students' perception of self-competence in STEM majors. Six students of grade 11 in an international school in Hangzhou, China, were interviewed to collect detailed knowledge of their perception of self-competence in STEM fields and the influence their parents, teachers, textbooks and social media have on their ability perception in these fields and career aspirations. The change of which factors may ameliorate the self-competence of high school students will also be analyzed. This study discovered that girls' parents more frequently hold gender-stereotypical opinions regarding girls' abilities in STEM subjects. This stereotype will significantly undermine a girl's self-competence and prevent her from delving deeper into STEM fields. For girls, same-gender teachers typically hold fewer gender stereotypes regarding their STEM capacities and can serve as great STEM role models that inspire and boost girls' confidence. The international students perceived almost no gender stereotypes in their teachers. The learner profiles emphasized by the IB diploma programme in school have helped students develop prominent critical thinking abilities and allowed them to rationally evaluate gender stereotypes related to female STEM competence in social media and textbooks. Based on the results, several suggestions to help eliminate the influence of gender stereotypes regarding STEM competence on students and create an equal development environment for them are also provided.