This study use Laser ultrasonic technique (LUT) and finite element method (FEM) to characterize the anti-symmetrical flexural (ASF) modes propagation along wedge tips with a natural crack. The mode convertion (MC) will emerge when ASF wave encounting a defect on the wedge tip. Reflection coefficient (RC) and transmission coefficient (TC) are obtaind from energy ratio that calculated from simulation and measurement results with different defect depths and different crack's shape on the wedge tip.