In traditional seismic analysis studies, transmission towers are usually assumed to be fixed on the ground, neglecting the soil-structure interaction (SSI) that may lead to inaccurate seismic performance evaluation of transmission towers. A comprehensive analysis of the seismic response, collapse damage, and collapse vulnerability of an actual 1000- kV transmission tower was carried out, considering SSI under seismic excitations. In ABAQUS, the interaction between soil and pile was simulated by setting zero-length springs along piles. A finite-element model of the transmission tower considering SSI was also established. Based on the numerical model, the dynamic characteristics and structural dynamic response of the transmission tower were analyzed. The impact of SSI on the collapse mechanism and vulnerability of the transmission tower was studied using the incremental dynamic analysis method. Results show that the vibration modes of the transmission tower with and without considering SSI are similar, but the natural frequencies differ greatly. Ignoring SSI will lead to underestimating the seismic response of the transmission tower and overestimating its collapse resistance. Therefore, studies considering SSI can improve the seismic capacity of the transmission tower, thereby ensuring the safety of the transmission line.