Abstract:Generally,when the variation of density of medium is smaller than that of velocity,it can ap-proximately take the density as constant and using acoustic equations and velocity functions to describe wave is feasible;but when the variation of density of medium is equivalent to or greater than the variation of velocity,the variation of density can’t be neglected?the acoustic equations do not reflect the influence of density function on wavefield.Starting from the basic equations of elastic dynamics,the paper deduced full P-wave equations m non-homogeneous medium and its finite-difference format.The right items of full P-wave equations include spatial variation item of pressure field and spatial variation item of density and completely describe the role of two factors velocity and density during waving.The numeric computation showed that the simulated results by full P-wave e-qu at ions could more accurately describe the feature of wavefield when studying reflection and transmission in non-homogeneous geologic body and on interface of beds.The analyses of relevant simulated results were conducted in combining with analytic solution of reflection and transmission issues in the paper * which pointed out that it should use the conception of impedance or impedance rate in reflection issue when there is distinct difference of density on both sides of interface.