Abstract:An extreme daily rainfall (maximum of 1056.7mm) induced by a long-lived linear-shaped mesoscale convective system (β-MCS) occurred over Gaotan town (GT) of Guangdong province during 30-31 August 2018, which broke the historical record in Guangdong province, caused severe flash flood and aroused social concern. Based on multiple observation data and NCEP/NCER_FNL reanalysis, we performed properties of the precipitation, convective systems evolution, synoptic and meso scale environmental conditions, initiation and maintenance of the β-MCS. It is shown that tropical cloud clusters move northward and induce large-scale heavy rainfall, with background of monsoon depression as well as mesoscale favorable environment of high-thermal, high-humidity. Extreme rainfall over GT is caused by a linear-shaped β-MCS, characterized by back-building, over-long-lived, quasi-stationary, low echo-top-height and low echo-convective-centroid. Organization of β-MCS is closely related to near-surface wind field, which is affected by multi-scale systems that we qualitatively analyze using rotation rate equation of sea and land breezes. The southerly flow is able to sustain for a long period that is determined by the forcing of multiple interaction, that monsoon depression and local terrain induce southerly flow to rotate counterclockwise, but barometric gradient induces southerly flow rotate clockwise, and take a balance finally. Southerly flow on the side of river valley HJ over slope terrain strengthening helps the warm-ridge development of temperature field, blocking cold pool outflow boundary move southeastward on the side of mountain over slope terrain, leading to sharp temperature gradient over that region. Quantitative diagnosis using mesoscale atmospheric dynamics equation shows the dynamic mechanism to sustain convection maintenance and β-MCS organization stems from local vertical wind shear, causing by the sharp temperature gradient.