In the midnight of 2 August 2015 and the early night of 9 August 2011, extreme flashrain events were observed in the Taihang Mountain area under the background of different weather systems. The thunderstorms strengthened in the Taihang Mountain area, and extremely heavy rainfall were observed in Pingshan Station and Shijiazhuang Station in 2 h. Based on routine upperlevel and surface observation, automatic weather station (AWS) data and Doppler weather radar data, the reasons of the extreme flashrain impacted by Taihang Mountain with different backgrounds are analyzed. The results show that easterly air flow is forced to uplift in the mountains, then encountered with thunderstorm outflow forming mesoscale convergence line to trigger new thunderstorms. Local heavy rainfall is affected by the backward propagation characteristics and train effect of radar echo. Convergence ascending motion and vertical wind shear are enhanced by the Taihang Mountain terrain strengthening thunderstorm in the process of going down the mountain. The Taihang Mountain terrain plays different roles in the development of thunderstorms under different weather systems. Under the guide of westerly flow, extreme heavy rainfall is triggered by a gust front in warm sector, charactered by abruptness, short time and strong winds. Thunderstorm outflow down mountain is accelerated and convergence with piedmont easterly wind is strengthed to trigger new thunderstorms, being combined with the downhill flows and forming extremely heavy rainfall in the hilly region. However, under the guide of northeast flow, extreme shorttime heavy rainfall triggered by reflux cold front and gust front features longer duration, heavier rainfall, and weaker wind. Northeast cold wet reflux is resisted by east slope of Taihang Mountain. The western end of the thunderstorm outflow boundary from NNEward is forced to uplift on windward slope to trigger and strengthen thunderstorms. Northeast airflow turns its direction in cyclonic deflection and the thunderstorms flow down to the southeast, so that convergence with the easterly wind in plains is strengthened, making the total time of rainfall longer and precipitation greater in hilly areas and piedmont.