Abstract: A nocturnal bow echo under the warm and moist environment in front of the upper trough caused short-term severe rainfall and gust on 13-14 July 2012 is analyzed and simulated using a mesoscale model. The bow echo with high precipitation efficiency merged from two thunderstorms of multiple cells in the high humidity and strong low-level vertical wind shear environment. The long distance gust appeared along the bow echo's path from Jiaxing to Qingpu and Baoshan, Shanghai. The mid-level entrainment of dry and warm air which came from the southern subtropical high was the critical environmental element that strengthened downdraft through evaporation and cooling. The maintained sloping-downward rear inflow jets (RIJ) in the rear part of bow echo together with the downdraft strengthed the pressure gradient of the leading edge of the bow echo, which were the critical causes of the strong gust of the bow echo. Two mechanisms for the bow echo's develpoment and maintenance are found: the strong low level environmental wind shear prevented the cold pool from leaving the bow echo; and a vortex pair caused by strong outflow (gust front) and strong environmental vertical wind shear made the new convection develop vertically at the leading edge of the bow echo.