If the Eiffel effect is not considered in mechanical analysis of transmission towers, the computed result may be different from their actual force conditions. Based on the Eiffel formula in 《Code for Design of High-rising Structures》（GB50135-2006） and the geometry of power transmission towers, an Eiffel effect formula is deduced that can directly make use of the results from transmission tower computation software TTA and a corresponding computation program is written for calculating the Eiffel effect that can calculate the force of the tower members and select member materials.