This paper describes development of method for estimating dynamic characteristics of unbalanced wire tension acting on overhead line equipment in natural wind. The unbalanced wire tension is the cause of fatigue of overhead line equipment, and this study evaluated this load. In order to clarify dynamic characteristics, field tests were conducted in two sites where experience strong northwesterly winter winds and fatigue of overhead distribution equipment was actually observed. From field test data, it was found out that turbulence of the wind speed produces an unbalanced wire tension acting on overhead distribution equipment, and this loading has certain fluctuating characteristics. Then, the field test data was normalized by various line characteristics, which were span, sag, and angle between wind direction and the line, based on a wire tension equation. General characteristics of the unbalanced wire tension were revealed by a statistical analysis based on a normalized unbalanced wire tension. A statistical analysis for normalized unbalanced wire tension amplitude calculated with the rainflow method clarified that the amplitude and frequency have a strong correlation with wind speed. This study developed a distribution model of the amplitude of the unbalanced wire tension and established a method for estimating the unbalanced wire tension.