||The South China Sea(0-25°N, 99-121°E) oceanic circulation is investigated by dynamic analyzing techniques based on the concept of vorticity and vorticity balance, through employing a three dimensional primitive equation ocean model. Vorticity equations are derived for tracing vorticity integrated for certain defined geometric layers and for dynamic active regions. In particular, the results obtained from the vorticity dynamic equation integrated in the upper 200m depth, where active currents exist, are examined. Focus is put on the circulation field in the regions around Luzon Strait and to the east off Vietnam coast, where Kuroshio intrusion and coastal jet separation occur, respectively. It is found that the absolute vorticity tends to be conserved at the Luzon Strait, while vorticity off Vietnam coast is considerably regulated by wind stress curl. In addition, vorticity is used as a geometric parameter to identify currents, eddies and separation. It is found that major currents in the South China Sea can be indicated by the curl on directional flow (vordir= ∇̅ x v⃗/IvI⃗, v⃑ = ui⃑ + vj⃑). The method amplifies the directional shear of the major currents at their boundaries. It is shown that the quantity J(u,v) / (∇̅⋅v⃗)2 obtained from divergence, ∇̅⋅v⃑ ,and Jacobian, J(u,v)= ∂u/∂x*∂v/∂y-∂v/∂x*∂u/∂y are generally relevance to the identification of eddies and current separation. Near eddy's centre, a relation between vordir and Jacobian is built. Finally, calculation which links the geometric quantities(vorticity, divergence and Jacobian) to physical quantities are also presented to better understand dynamics in flow field.