Abstract: Large height differences often occur in the tower layouts of overhead transmission lines in hilly areas. To standardize the tower selection method under such conditions, comparative calculations reveal that the theoretical vertical span closely matches the horizontal distance between the lowest points (sag) of conductors on both sides of the steel pipe pole in the positioning diagram. However, due to the presence of virtual spans, it is meaningless for calculating vertical loads, indicating inaccuracies in traditional tower selection methods. Through analysis of typical steel pipe pole cases, it is concluded that the vertical span has a minimal impact on the strength of straight steel pipe poles. When the maximum design wind speed is 25 m/s and the actual horizontal span is 70%, 80%, or 90% of the design horizontal span, the converted actual vertical span becomes 4.5, 3.4, or 2.2 times the design vertical span, respectively. These findings broaden the design approach for selecting straight steel pipe poles under large height differences and provide a reference for straight angle steel tower selection.