A numerical experiment was adopted to analyze the effects of wind speed, initial wind angle, elevation difference and ice thickness on the longitudinal unbalance tension of transmission tower. Harmony-superposition method was used to simulate the fluctuating wind speed time series acting on the transmission tower line, and the law of unbalance tension was derived by changing elevation difference and ice thickness.The results have shown that, in some cases, the value of the longitudinal unbalance tension of the tower in existing electricity industry standard is smaller. Based on computational analysis, the theoretical formula of the longitudinal unbalance tension of towers subjected to wind and snow simultaneously was proposed. The errors of the formula are within ± 6% compared with numerical simulation. It has preferable accuracy.