Abstract: An extreme gale event, hereinafter referred to as "6.1" gale event, occurred in Jianli, Hubei on 1 June 2015, which is triggered by downburst and caused the capsizing accident of cruise ship "Dongfangzhixing". Using data from conventional meteorological observations, intensive automatic weather station, radiosonde, Doppler weather radar and NCEP reanalysis, we have analyzed the environmental conditions and influencing systems of the "6.1" gale event, with special emphasis on analyzing its cause based radar data. Results are as follows. (1) The "6.1" gale event occurred under some favorable conditions such as strong low-level vertical wind shear and lower-than-normal convection condensation level, and it is triggered by the development of mesoscale vortex at ground level and cold front. (2) This event is caused by linear multicell storm, in which there are accompanied by the supercells and emerged mesocyclones within the serial volume scans. (3) Mesocyclones revolved in high-speed and their bottom descended continuously after the storm cells developed into supercells, which can be the indication of tornado. (4) The development of a high value center of velocity at low elevation was observed during and prior to the occurrence of the extreme gale (hereinafter referred to as "extreme gale") caused by the downburst that led to the capsizing accident of cruise ship "Dongfangzhixing". The characteristics of mesocyclone in the storm cell have not been clear when the extreme gale occurred. In addition, strong reflectivity factor core descended continuously within the five serial volume scans before the extreme gale. (5) Radar radial velocity, storm quality charts and mesocyclone quality charts are important indicators for the early warning of the "6.1" gale event. And storm evolution, mesocyclone quality charts and high value center of velocity at lower elevation angle all can be certainly served as a reference before the extreme gale occurred.