According to the depth, the South China Sea can be divided into three boxes by a pycnocline and a sill. The upper homogeneous layer with 0–50m depth is taken as Box I; the 50m depth is characterized by the pycnocline. Box II lies between 50m and 2000m. Below 5000m is the deep basin water referred to as Box III. Based on the box model, and using the data of the amounts of particulate phosphorus in Box I, Box II and Box IIII, the consumption fluxes of dissolved oxygen have been calculated to be 4.4×10¹⁰ μmol/s in Box I; 78.3×10¹⁰ μmol/s in Box II, and 0.55×10¹⁰ μmol/s in Box III. Meanwhile, the average rate of oxygen consumption has been estimated to be 2.5×10^-7 μmol/(dm³s) in Box I; 1.8×10^-7 μmol/(dm³s) in Box II; 0.033×10^-7 μmol/(dm³s) in Box III. The value for Box III is very to close that calculated using a vertical shift-eddy mix model, based upon the vertical distribution patterns of the potential temperature and the dissolved oxygen content.

Using the equations of mass conservation for dissolved oxygen, incorporating the data sets obtained in 1984–1994, the fluxes of dissolved oxygen in Box I, Box II and Box III have been calculated; the box model of dissolved oxygen in the South China Sea has been established.

The total input flux of oxygen in the south china sea is calculated to be 280.4×10⁴ mol/s, of which 49.2% is from the adjacent oceans, 30.3% is derived from organism photosynthesis, 3.0% is from the rainfall, 0.4% is from the river water, and 17.0% is due to the interaction at the air-sea interface.