Flow experience plays a major role in influencing students' interest of STEM, which is the key to promote STEM talent development. Various teaching behaviors contribute differently to student learning performance and flow experience. Specifically, this research sought to concretely explore the different influences of Autonomy-supportive (AS) teaching behavior and Controlling (C) teaching behavior on students' STEM learning performance and flow experience. The research conducted an experimental exploration of STEM project among primary school students in two groups with two different teaching behaviors (AS and C) respectively. T-test and ANCOVA analysis revealed that both teaching behaviors greatly contributed to improvement of students' learning performance. MANCOVA analysis showed that students in Autonomy-supportive group got slightly significant higher flow experience than those in Control group. Regarding flow constructs, both groups had the similar level of engagement, but students in Autonomy-supportive group had higher enjoyment, and stronger control than those in the other group. In other words, Autonomy-supportive teaching behavior and Controlling teaching behavior both enhanced greatly students' STEM learning performance. While Autonomy-supportive teaching behavior allowed students to be more enjoyable and have a higher level of control in STEM learning.