Abstract:A meso γ scale and meso β scale downpour took place at Niutouya town of Funi ng County that located in the western bank of Bohai Sea from 5:00 to 6:00, o n 11 August, 2008. The same thing also happened in Tanghai County， and their pr ecipitations all exceed 100 mm per hour. Using CINRAD/SA radar data in Qinhuangd ao and in Tianjin, the physical quantity field of the mesoscale meteorology, MM5 model output, in Shanhaiguan, the synchronous data of the dense observations recorded once per minute, the relationship between meso β scale echo band and the peak value of the precipitation was analyzed. The tentative result shows that the downpour is resulted from the mutual perturbation between the mes o β scale system and the meso γ scale system under the background of the mes os cale echo band in the same matrix at different time. The former is the common mu lti cell storm with the distance of 100km away from the matrix of echo band. It can spread in wave form on the space profile of 300km, and is related to stirri ng of gravity wave. The latter is the strong multi cell storm, which would emer ge later on the bottom of the matrix of a weakening echo band, involved in the p erturbation of weak shear and the thermodynamic factor. The scale defined is fo und on radar GPS positioning of the centroid and GIS information proofing in the dense observational network. The predictable factors of meso small scale syste m on disastrous downpour have been explored 0—1 hour before its occurring in th e coastal zone, so that they can provide some prediction basis for early warning .