This intuitive and easy-to-use least-squares fitting demonstration tool supports inputting arbitrary data point matrices and target vectors, quickly calculating and visualizing the least-squares solution, prediction results, and residual vectors. The app graphically displays the fitting results, helping users gain a deeper understanding of linear regression and fitting principles. Results can be exported as PDF reports, facilitating teaching, learning, and scientific research archiving. It also features a built-in history record function that automatically saves each fitting data and results, supporting viewing, exporting, and deleting operations. It is suitable for teaching mathematical modeling, data analysis, and linear algebra.