Abstract:To enhance the understanding of the squall line maintaining mechanism under influence of Hangzhou Bay, the diagnosic analyses are made on the squall line in northern Zhejiang on 27 July 2014, using Doppler radar data, convectional and densely observed surface data and NECP GFS data. The focus is on the evolution of convection that moved into Hangzhou Bay from the north and the south coasts and its effect on the overall development of squall lines. The result indicates that the north south convergence lines and moderate strength of deep vertical wind shear are the key environmental factors of the generation and development of the squall line event. Convections are strengthened after moving into Hangzhou Bay from the north and the south coasts, leading to squall line maintaining. The better moisture conditions and unstable energy conditions in Hangzhou Bay result in the further strengthening of convection from the north shore of Hangzhou Bay, and the connection of two linear convections in southern Jiangsu, northern Zhejiang as well as the sustainable development of the squall line. The temperature and humidity on the surface of Hangzhou Bay is equal to the surface of south coast， and the strong wind shear in Hangzhou Bay leads to the maintaining strength of the convection into Hangzhou Bay from the south coast. Under the interaction of cold pool and rear inflow, bow echo develops on the sea, becoming an important factor for the maintenance of the squall line.