Abstract: In this paper, the theoretical method of calculating the axial radiation sound pressure of rectangular plate bending vibration under free boundary condition is deduced by using the numerical calculation and finite element method. This method can not only calculate the axial radiation pressure for a single flat rectangular plate radiator, but also for the stepped rectangular plate radiator. Taking the single flat rectangular plate radiator and a stepped one as examples, the variation of the axial pressure with the axial distance is calculated and tested. In addition, the relationship between the axial pressure and the input power applied to the transducer is also tested. It shows that in the near field of the radiator, the axial pressure fluctuates significantly with the increase of distance, and the maximum and minimum values of the sound pressure appear repeatedly; in the far field of the radiator, the sound pressure decreases slowly with the increase of distance; for different input powers, the variation trend of the axial pressure with the distance is the same, which further proves the correctness of the calculation method described in this paper.