In this paper,a multi modal combination imaging method based on synthetic aperture focusing technique is proposed to address the laser ultrasonic imaging problem of internal fatigue cracks in titanium alloy. The scanning laser source method is employed to extract time domain mode echo signals from different detection positions. By analyzing the amplitude distribution of reflected longitudinal waves and reflected shear waves in the B scan image,the temporal characteristics of crack echo signals are partitioned and recombined. Furthermore,inversion focusing is applied to accomplish the recognition and image reconstruction of internal cracks. The feasibility of this approach is demonstrated by conducting numerical simulations of the internal crack imaging process in titanium alloy plates using COMSOL Multiphysics,and its viability is further validated using MATLAB image algorithms. Compared to single mode wave imaging,the imaging method that combines reflected longitudinal wave and reflected shear waves effectively reduces artifacts,enabling accurate localization and image reconstruction of internal cracks. The relative errors of the reconstructed crack positions in the X axis and Y axis are both within 3%.