Abstract: The mathematical model for mould-filling under countergravity has been pro-posed on the basis of the principle of momentum.Dynamic processes of mould-filling are ob-served by means of high speed photography.The results have shown that the mould-filling under countergravity can be described by second order nonlinear differential equations,characterized by the dynamic damping oscillation.The velocity oscillation amplifies ae the pressing speed increases,if the pressure differential functions are of the same type,otherwise,it will depend upon the ascending properties of the functions.