Abstract: In this paper, solutions for travelling waves are derived with a partially nonlinear dynamic model with two dimensional internal gravity waves to 1) study forms, characteristics and velocity with which the cold surge propagates in the South China Sea during winter monsoon, and 2) discuss the contribution to the propagation by large scale meridional circulation and its vertical structure. thermodynamics, stability of stratification and initial disturbance. Important conclusions are that the cold surge propagates in the form of travelling gravity waves of no or weak dispersion with non-linear effect and much faster in the southward directin than the velocity of advection but almost as fast as that of internal gravity waves; condition of initial disturbance, subject to difference in flow fields and geopotential temperature, determines whether the cold surge travells in the form of preiodic or isolated internal gravity waves, which is reflecting two synoptic processes, and basic condition for the cold surge to travel in the form of propagating internal gravity is the strengthening and southward advancement of meridional circulation, stable atmospheric stratification, and weak convective condensation and heating.