Abstract: On July 12, 2014, a squall line formed across Tongxiang, Zhejiang. Strong gust winds appeared in Yuanfeng and Jinniu villages and resulted in human casualties and property damage. Through the survey of the disaster, the analysis of environmental conditions and echo characteristics on Hangzhou and Huzhou Doppler weather radars, it is shown that a tornado was produced by a strong cyclonic circulation which had developed associated with the squall line. The strong cyclone occurred in the forefront of the convex portion of bow echo below 1km. The increase of the best convective available potential energy (BCAPE) and storm relative helicity (SRH), and the decrease of lifting condensation level enhanced the likelihood of tornado. The strengthening and sinking of southwest jet together with the mid- and high-level cold air helped trigger the storm.