Pythagoras' theorem is one of the fundamental theorems of flat geometry in mathematics that students have problems in using it in new situations. The purpose of this article is improving students’,performance in using the Pythagorean theorem and fixing their misconceptions by 5E teaching model. The following article was a qualitative research based on action research method. Based on purposive sampling, 10 high school students of Allameh Tabatabaei in Shahrekord city were selected as the sample. The findings of this study showed that the use of 5E constructivist model led to deeper learning, fixing students’,misconceptions and improving their performance in solving problems related to the Pythagorean theorem.