This study shows a development of simplified model for a transmission line tower considering influence of adjacent transmission line towers. Two types of models are prepared. One is single tower model without transmission lines, another one is continuous three towers model which consist of a central transmission line tower and two adjacent transmission line towers. These continuous three towers are connected with transmission lines including overhead ground wire. Eigenvalue analysis and dynamic response analysis were conducted using these two models. Differences of vibration characteristics and dynamic behaviour between both models were compared based on the obtained analysis results. The influence of adjacent transmission line towers was clarified. Transmission lines greatly affect the seismic response of central tower in longitudinal direction at the time of earthquakes.