辛普森（Simpson）公式是牛顿-科特斯公式当n=2时的情形，也称为三点公式。辛普森公式是利用区间二等分的三个点来进行积分插值。其科特斯系数分别为1/6，4/6，1/6.-The paper points out the defects of the const pressure wave velocity method and do some improvements on it: rebuilding the expressions of the pressure wave velocity in accordance with the Simpson s rule.