超声成像检测技术在现代工业无损检测中具有重要地位，已成为定量检测的重要手段。提高分辨率是目前超声成像的发展方向，成像分辨率是评价超声成像系统的重要的性能指标之一。但超声波在被检测物体中传播时，探测的深度与获得高分辨率是一对固有的矛盾，即高频超声系统的分辨率高但穿透深度浅，低频超声系统的分辨率低但其穿透深度深。通过对合成孔径的成像原理、成像算法、方位分辨率等问题的分析，从理论上论证了合成孔径成像的分辨率只和孔径的大小有关，而和脉冲频率的高低没有关系，阐述了应用合成孔径技术在超声波无损探伤系统的可行性。通过Matlab对单阵元合成孔径聚焦波束和多阵元合成孔径聚焦波束进行了仿真，为今后的实际应用提供了依据。

Ultrasonic imaging detecting technique plays a very important role in the field of nondestructive testing in modern industry and it has become an important method for quantitative detecting. Nowadays ultrasound imaging technique is developed to enhance resolution ability. The sound imaging resolution ability has become one of the important performance indexes in evaluating ultrasound imaging system. But it is contradictive between the detectable depth and resolution when taking use of ultrasonic to detect object. In other words, it will get lower detective depth with high frequency ultrasonic system and it will also get lower resolution with low frequency ultrasonic system. Through the discussion in SAR imaging principle, imaging algorithm and orientation distinguishing etc., a theoretic result that imaging resolution is just related with aperture and no related with pulse frequency was demonstrated. It is also revealed the feasibility of applying the SAR theory in NDT system. Beam for single-element synthetic aperture and multi-element synthetic aperture were simulated through Matlab, whose result becomes basis for the future application.