Abstract: By using the principle of reciprocal work and the stiffness equation of the beam element in its local coordinate system, a simple and efficient method for construction of influence lines for internal forces at specified sections is established. By applying a set of virtual concentrated loads to the structure and performing a static solution once only, the desired influence line can be obtained. The main advantage of the present method lies in its high efficiency, which is especially true when calculating the influence lines for internal forces at some specified sections of large frame structures.