The Bay of Bengal (BOB), the largest bay in the world, forms the northeastern part of the Indian Ocean. Both the BOB and the South China Sea (SCS) were influenced by monsoon seasonally with similar latitude range. Primary productions (PP) of the two seas and their influencing factors were reviewed in this paper. The spatial distributions of PP and their environmental regulation mechanisms showed obvious differences between the two seas. Complicated physical phenomena could be found in the SCS, such as mesoscale eddies, coastal upwelling, Kuroshio, typhoon and river discharges. River discharges (especially those from the Pearl River and the Mekong river) and coastal upwelling (e.g. the Eastern Guangdong upwelling) bring abundant nutrients to the coastal waters in the southwest monsoon period, and result in the stimulation of phytoplankton growth. Mesoscale eddies (cold eddy or warm eddy) have different physical structures from adjacent waters, and can influence the nutrients availability. Kuroshio intrusion (characterized as warm and oligotrophic waters) and typhoon can also regulate PP in the SCS. Various physical processes could potentially control nutrient supply in the euphotic layer, and consequently influence the spatial and temporal variation of PP in the SCS. In the BOB, copious rainfall and river discharge often decreased salinity in the upper layers during summer, and sea surface temperature was warmer than in the SCS, leading to strong stratification in the upper layer. Weak wind over the Bay was unable to erode the strongly stratified surface waters; thereby the wind-driven vertical mixing was restricted within a shallow depth. This inhibits any possible introduction of nutrients from deeper water below the mixed layer into the upper layer. Meanwhile, suspended solids from the discharges and cloudy weather decreased light availability and therefore limited phytoplankton growth. In the near-shore area, river discharge and coastal upwelling can enhance PP in the SCS, while stratification in the BOB can inhibit algal growth in the euphotic zone, so PP in the coastal waters of SCS was higher than that in the BOB. In the open sea area, PP in the SCS is supposed to be close to that in the BOB. As a whole, PP in the SCS is evaluated to be higher than in the BOB.