New equation is derived from an object function by means of initial values af-ter the differential equation of deflection in the simply supported beam with step func-tion,and dirac function is laplace transformed and inverse transformed.

• 本文对含有阶梯函数、Dirac函数的简支梁挠曲线的四阶微分方程进行Laplace变换，然后再进行逆变换，求出原函数，最后利用边界条件推导并建立连续梁的新三弯矩方程。