Two successive longlived mesoscale convective systems (MCSA1, MCSA2) struck Pearl River Estuary of South China during 8-9 May 2014, and induced extreme precipitation over the region. From noon of 8 May MCSA1 sustained over than 11 h on land of South China, with slowly moving towards southeast from east of Guangxi to Pearl River Estuary in Guangdong. The successive MCSA2 sustained more than 9 h, inducing rainfall of more than 400 mm along the coast of the Pearl River Estuary from early morning to noon of 9 May. Weak cold surface layer sustained in the south of South China with weak surface temperature gradience on the morning of 8 May before the convection burst. The initialization of convection was connected with strengthening of surface south 〖JP2〗wind and topographic lifting near noon of 8 May. MCSA1 evolved from〖JP〗 training line/adjoining stratiform (TL/AS) to mesoscale vortex in convective organization under weak baroclinic environment. With propagation of surface cool pool due to MCSA1’s precipitation in the early night of 8 May, surface temperature boundary and wind convergence zone was pushed to the southwest coast of Guangdong. In the late night of 8 May MCSA1 moved out of land, then MCSA2 was developing adjointly to the remnant cool pool boundary induced by MCSA1 with lowlevel southwest wind enhancing in the early morning of 9 May. MCSA2 was composed by multiple parallel mesoβ scale linetype convective systems, the extreme rainfall was related with quasistationary cool pool boundary, trainmoving cells in mesoβ scale linetype convective systems with high precipitation efficiency. From late night of 8 May to morning of 9 May, the balance between cool pool outflow and lowlevel vertical shear could sustain upright convective cells of MCSA2. In conclusion, with carefully researching on convective feedback to boundary and surface layer, the forecast skills could be improved for heavy rainfall events in weak synopticforcing environment during the prerainy season in South China.