Science teachers play a key role in successfully implementing science education reforms and providing all students with meaningful science learning opportunities. Therefore, what core teaching competencies do science teachers need to have in their practice? This study uses fuzzy Delphi technique and Analytic Hierarchy Process to approach the above problems. Experts from Chinese universities, secondary schools and educational research institutions were invited to participate in two rounds of Delphi process. The research results show that the four domains of core teaching competencies of science teachers and their 21 competencies have high content validity. Additionally, it can be concluded that the weights of core competencies of making learning objectives, raising pedagogical questions, stimulating learning motivation and analyzing course content ranked high, while the weights of core competencies of using information technology and multimedia, evaluating practical work, and presenting research results have received less attention. It is believed that the results of this study can enlighten the education reform of science teachers and promote the professional development of pre-service/ in-service science teachers.