The invention relates to an implementation method for a mixed absorbing boundary condition applied to a variable density acoustic wave equation. The implementation method comprises the steps of dividing a whole simulation region into an internal region and a boundary region, calculating the wave field value of a sound wave of each absorbing boundary layer by using the variable density acoustic wave equation and a variable density AWWE (Arbitrary Wide-angle wave equation) respectively, and performing linear weighting on the two calculation results to obtain the wave field value of the sound wave of each absorbing boundary layer. On the basis of realizing a single variable density AWWE absorbing boundary layer and in 2D (2 dimensional) and 3D (3 dimensional) space coordinate systems, the wave field value of the sound wave of each absorbing boundary layer is calculated by respectively adopting a combination mode of processing edges of the variable density AWWE and processing angles of a modified 15-degree one-way wave equation, and a combination mode of processing faces of the variable density AWWE, the processing edges of the modified 15-degree one-way wave equation and the processing angles of a 5-degree one-way wave equation, and the mixed absorbing boundary condition of the variable density AWWE is realized. The implementation method can be widely applied to the numerical simulation of constant density and variable density acoustic wave equations.