According to the data, there are more than 1000 algorithms for the equal area method of Pythagorean theorem in the first volume of eighth grade mathematics. Now, a common algorithm is to put four congruent right-angled triangles into a square with the hypotenuse as the side length. There is a small square in the square, and its side length is exactly the longer right-angled side of the right-angled triangle minus the shorter right-angled side. Then pythagorean theorem can be deduced by using equal area method and exhausted square formula. Let A and B be right-angled sides and C be hypotenuse, then the square of C is the area of a big square, 2ab is the area of four right-angled triangles, and the square of the difference between B and A is the area of a small square.