The kinetic model based on SCFAs metabolism was applied for the prediction of phosphorus-and glycogen-accumulating organisms (PAO and GAO) competition with different carbon sources and m(P)/m(COD) ratios. When acetic acid was used as the sole carbon source, the biomass compositions were almost the same as those before cultivation, and neither PAO nor GAO could be out-competed from EBPR. However, increasing propionic acid in the influent helped PAO to be the predominance organism, and EBPR performance kept excellent when the ratio of propionate to mixed acids (acetate + propionate) was higher than 0.33. It also found that the m(P)/m(COD) ratio should be kept at 0.04-0.10 to avoid phosphorus became a limiting factor for PAO growth. This was because at low m(P)/m(COD) ratios, such as 0.01, GAO would take up 95% of the total (PAO + GAO) biomass.