Transmission towers with unequal-length legs, commonly used in the mountainous regions of Southwest China, are particularly vulnerable to structural damage caused by rockfall impacts. To evaluate their dynamic behavior under such conditions, an 800 kV unequal-length-leg transmission tower was simulated using the Abaqus finite element software. This study investigates the tower’s response to rockfall impacts under various scenarios and compares these responses to those of conventional transmission towers. The results indicate that rockfall impacts induce rapid structural responses and significant transient deformations. Both the mass and velocity of the falling rocks are critical factors influencing the tower’s behavior. Peak displacements initially decrease with height but show an increase at higher elevations. Compared to conventional towers, the legs of the unequal-length-leg transmission tower exhibit higher stiffness, leading to reduced deformation and greater acceleration during impacts.