This study investigates a long-duration mesoscale convective system (MCS) with extreme rain-fall (451 mm in 16 hours) over the western coastal region of Guangdong on 10 May 2013 during the Southern China Monsoon Rainfall Experiment (SCMREX).The environmental conditions are characterized by little convective inhibition, moderate convective available potential energy, moderate precipitable water, low lifting condensation level, and lack of low-level jets from the tropical ocean.Repeated convective back-building and subsequent northeastward "echo training" of convective cells are found during the MCSs early development and mature stages.However, the earlier and later stages possess distinctive initiation/maintenance factors and organization of convection.During the earlier stage from midnight to early-morning, convection is continuously initiated when weak south-easterly and southerly flows near the surface impinge on the east sides of Mts.Longgao and Ehuangzhang (with their respective peaks of approximately 800 m and 1300 m) and moves northeastward, leading to formation of two quasi-stationary rainbands.During the mature stage from early-morning to early-afternoon, new convection is repeatedly triggered along a precipitation-induced cold outflow boundary, resulting in the formation of several rainbands that are quasi-stationary and move east-ward in later times.Individual rainbands during the stages similarly consist of northeastward training of convective cells and a stratiform region to the northeast.While the MCS dissipates, a stronger squall line moves into the region from the west and passes over within about 3.5 hours, contributing about 10% ~ 15% to the total rainfall amount.It is concluded that terrain, near surface winds, and convectively generated cold outflows play important roles in initiating and maintaining the extreme-rain-producing MCS.