Abstract: Using conventional observation data, automatic station data, Sanya radar data, NCEP reanalysis data and GFS forecast data, we analyzed a thunderstorm that affected Sanya on 9 May 2019.The results show that the upper dry cooling trough and the lower southwest warm and humid air, a mesoscale convergence line formed by the northeast land breeze and the weak southwest sea wind provide good conditions for the process of water vapor, thermal instability, dynamic uplift and triggering.The development and merging of mesoscale convective organization are the key to the maintenance of convection.Strong wind inflow behind convection and scattered weak echo line in front can provide a good early warning for the occurrence of thunderstorm and gale.