The invention provides an earthquake forward modeling method applicable to non-uniform motion water bodies. The method comprises the steps that firstly, data, observation systems and hypocenter parameters related to seawater and strata are acquired; secondly, starting from the mass conservation equation, the Euler equation and the adiabatic state equation, through an asymptotic method and a suitable assumption based on the seawater practical conditions, a first-order stress-velocity equation suitable for the non-uniform motion water bodies is derived; thirdly, a reasonable boundary condition is given; finally, a control equation and the boundary condition are discretized through high-precision finite difference, and the propagation process of seismic waves in the seawater and seabed elastic media is simulated. According to the method, the influences of the density, sound velocity and flow velocity in the seawater on propagation of the seismic waves are comprehensively considered, the propagation condition of the seismic waves in a complex marine environment can be truly reflected, and the method has high application value in marine oil-gas exploration, especially deepwater oil-gas exploration in the complex marine environment.