Abstract: To consider the effect of the rigid zones of joints made of stiffeners and connecting plates on steel tubular transmission towers efficiently and accurately, the main member is seen as a combination of several beams with different sections. Firstly, the formulations for the area and inertia-moment of the cross section of the rigid zone on the either side of main members were derived. Secondly, based on energy theorem, the element matrix of a variable section beam is achieved, and the open source software OpenSees by C++ is introduced. Finally, the results by the finite element models where the main members and the rigid zones were simulated by varied-elastic modulus beam elements, and the constant section beam elements, variable section beam elements and shell elements were compared. It shows that: the constant section element underestimates the moments and the maximum stress of main members, while the variable elastic element underestimates the displacement of a tower. They all lead to the unsafe design of a tower. The results by a variable section beam and shell elements are very close to the results by the experiment, while the calculation expense is much less than the former. Therefore, the efficiency and the accuracy of the variable-section beam element model are proven.