Abstract: The coefficient of fitting curve is the same whether it is calculated by the cumulative scoring or the deflection curve of beams with sleek curve and calculating according to the characteristics of deflection derivative and boundary conditions and the continuity conditions of beams.The later method is of great physical significance.It not only applies to the deformed calculation of both statically determinate beams and statically indeterminate beams,statically indeterminate beams but also needs no equation of bending moment.