Abstract: This paper introduces the principle of least square (LSQ) method, designs the source code and detail experimental solution for the propose to address the issue of regression by LSQ, visually shows the methods and steps and effects of addressing issues by LSQ, and inspire students to observe, compare and analyze these results. The experiment makes it easy for students to understand LSQ , helps students to deeply understand machine learning principle, master the machine learning method, and grasp the essence, reasons and elimination strategies of overfitting and underfitting. Furthermore, the experiment enhances students’ ability to analyze and solve the problems, and solve practical problems using LSQ.