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The meteorological causes of wind deflection and tower collapse of a 500 kV transmission lines are analyzed. The wind speed distribution characteristics in the fault area of the line are obtained by using the observed wind speed of an automatic weather station and the three-dimensional wind field based on radar inversion. The results show that the maximum wind speed and the extreme wind speed observed by automatic weather stations around the two accidents are small. The three-dimensional wind field of radar inversion better indicates the fault's location and time. Compared with strong convective weather which can cause the wind deflection， the strong convective weather which can cause the tower collapse has a higher echo height and stronger updraft. The core height of its reflectivity factor drops more than 3.5 km within 6 minutes， causing greater ground damage， but its locality is strong and the influence range is small. The results show that the current design wind speed of the transmission line is safe under the strong convective weather that causes wind deflection， but adverse terrains that can accelerate the wind speed must be avoided. It is suggested to take “cascaded collapse prevention” as the main idea for the microburst which can cause the tower collapse. In addition， under the influence of strong convective weather， the gust coefficient calculated by the observed wind speed is significantly larger than the value in the relevant specifications.