The existing researches for wind load characteristics of the downburst mainly concentrated on stationary impinging jet model，but rare investigation was for time-varying characteristics and the impact of mountain terrain. In this paper，based on the impinging jet model，the decay function was brought in to make the inlet wind velocity more close to the decay process of the whole life cycle of the thunderstorm，and the wind load characteristics of typical high-rise buildings on the top of the slopes and the characteristics of the thunderstorms on the slope landforms were analyzed by transient large eddy simulation (LES). The results show that the transient simulation of LES is more reliable，the wind speed fluctuation of the unsteady shock wind field is larger，and the variation law is similar to the measured wind speed curve. The unsteady wind load shows strong unsteady characteristics，greater fluctuations and rapid attenuation with wind speed. The wind load fluctuation of unsteady shock wind is wide and has strong potential to damage，the wind load on the sloping terrain is generally smaller than that of the flat ground，and the influence of the slope terrain on the upper part of the building is obviously higher than that of the bottom. With the enlarging of slope angle，the upper wind load gradually decreases.