Abstract: In design the structural analysis is conducted to determine the internal forces of member,for unbraced structure the gravitational second-order effect due to structural sidesway and flexure of member must be considered, for braced structure the sidesway effect is not present.commonly,in the structural analysis only the internal forces at ends of member are found,and so the following problem must be solved,whether the flexural second-order effect will cause the moment at some section larger than the moment at ends.The flexural second-order effect for RC eccentrically compressed member was researched theoretically,the obtained results were compared with those of design code for RC structures．