In one-dimensional nonlinear system, linear parts of acoustic wave meet wave equation and nonlinear part is assumed similar to that of nonlinear Schrödinger equation. Transmission coefficients of two incident acoustic waves from opposite directions are calculated respectively. It is shown that this model has unidirectional penetrability for acoustic wave within certain frequency and amplitude, and expresses behaviors of diode. Increasing nonlinear intensity leads to a remarkable enhancement of unidirectional penetrability.