In [2], YIN Jing-rao gets the triangle inequality about simplex. This paper spreads the inequality , here A. B. C stand for the three interior angle of triangle ABC to n-dimensional simplex field and gets another class of inequality about dihedral angle: here,, is interior dihedral angle of leteral face F, and F,, m, n is arbitrary natural number. The equality is obtained when An is regular simplex.