The identification of transmission lines is critical for the intelligent inspection of unmanned aerial vehicle (UAV) along these lines, representing a challenging and popular area of current research. Traditional line identification methods, such as image recognition and electric field assisted identification, face significant obstacles. Image recognition methods easily cause accidents such as line loss, recognition errors, and even collisions between drones and towers when UAV passes over towers. Electric field assisted identification is hampered by the metal components on UAV and transmission line towers altering the electric field distribution around the lines, resulting in low accuracy of transmission lines identification. Therefore, this paper studies the spatial magnetic field distribution characteristics and trends of transmission lines, and focuses on research a transmission line identification method based on these magnetic field distribution characteristics, aiming to solve the difficult problem of transmission line identification during autonomous UAV inspections.