Nonlinear　ultrasonic　non-destructive　testing　(NDT)　is　a　widely　used　method　for　detecting　micro-damages　in　various　materials　and　structures　due　to　its　high　sensitivity　and　directional　capability.　However,　the　extraction　and　modulation　of　extremely　weak　nonlinear　ultrasonic　signals　is　quite　a　challenge　in　practical　applications.　Therefore,　this　paper　focuses　on　the　second　harmonic　modulation　signal　method　in　nonlinear　ultrasonic　NDT　and　proposes　the　design　of　the　phononic　crystal　filter　(PC　filter)　to　achieve　this　filtering　function.　Through　finite　element　simulations,　it　is　demonstrated　that　the　filtering　frequency　of　the　filter　is　influenced　by　the　structural　configuration,　material　wave　speed,　and　geometric　characteristics.　Then,　the　design　method　for　cubic　PC　filters　is　established.　Furthermore,　a　time-domain　finite　element　method　is　introduced　to　verify　the　filtering　ability　of　the　filter　and　further　validate　the　rationality　of　this　design　approach.