||Utilizing a three-dimensional, primitive equation ocean circulation model as well as field measurements, this study investigates time-dependent, three-dimensional variability of coastal upwelling, a prominent phenomenon with formation of coastal jet and upwelled cold and nutrient rich deep water at the surface, over a unique widened continental shelf in the northeastern South China Sea (NSCS) during summer 2000. The model is forced with realistic atmosphere momentum and heat fluxes, Pearl River freshwater discharge and with remote fluxes through downscale coupling. The results of simulation are reasonably well validated by the in situ and remote sensing measurements. As a result of circulation induced by upwelling favorable wind stress over continental shelf, an intensified coastal upwelling is formed over the widened shelf, and is dynamically sustainable under alternating upwelling favorable or unfavorable atmospheric and external forcing in NSCS. A series of numerical experiments and dynamic analyses have been conducted to identify the process and mechanism that control the variability of the coastal upwelling. It is found that the upwelling circulation over the shelf is well maintained by the topography of the unique widened shelf during the season with prevailing summer monsoon, as a result of persistent geostrophy balance between alongshore pressure gradient force and Coriolis effect. Besides the local wind forcing, we investigate the influence of remote forcing from South China Sea (SCS) and from East China Sea (ECS) on the variability of the coastal upwelling in NSCS. The variation of remote momentum flux from ECS has a much stronger control on the intensity of the upwelling in NSCS as compared with that from SCS. In general, the intensity and duration of upwelling unfavorable forcing during the summer are not sufficient to spin down the upwelling once it is established in NSCS.