The short-term destructive strong wind formed by the downburst near the ground will pose a greater threat to building structures, especially to wind-sensitive structures such as transmission tower-line systems. Based on practical engineering, a new finite element model for the transmission tower-line system is established. The deterministic-stochastic hybrid model is used to simulate the generation of the downburst wind field. Based on the Tian-Ma-Qu material model, the progressive collapse process of the structure under the downburst is conducted. The research results demonstrate that: the transmission tower under the downburst performs its significant local deformation in a short time, the buckling of many diagonal members and several main members is the governing reason for the entire collapse of the tower. The segment 6 of the tower is considered the weakest position, to which should be particularly paid attention in the design of the structural resistance to downburst.