Abstract: Using the simulation calculation of C language program, we find that the answer of exercise 13 （in ＂Schrodinger Equation＂, Chapter III of 《Modern Physic》 which is a 21st century institution of higher learning, written by Yang Gui-lin, Jiang Xing-fang, Ke Shan-zhe, printed by Science Press in 2004） is incorrect. The correct result through numerical calculation is obtained and this question is also discussed in detail.

Key words: two-dimensional infinite square potential well, degeneracy, quantum state, C language program, indeterminate equation