The simplest method of Jiugongge is simple and easy to understand. thank you

As shown in the figure, Jiugong is the axis symmetry of the upper, lower, left and right diagonals, and also the point symmetry of the center.

Arrange the numbers 1 to 9, from small to large, or from large to small. In a symmetrical position, the sum is 10, and the number 5 is right in the middle, which is the center of symmetry.

Therefore, the number in the middle green grid must be 5, the number in the corner blue grid must be even, and the sum of the numbers in the diagonal grid must be equal to 10. The remaining four white squares are determined by calculation. The sum of the number of three squares on the same line is equal to 15.