Abstract: By the control of element phase of the ultrasonic transducer array, flexible and controllable synthesis beam can be obtained to implement dynamic focusing and imaging detection. Higher detection sensitivity, resolution and SNR will be achieved. On the basis of deflection and focusing properties research of the ultrasonic array transducer sound field, the constant sound path focusing model is designed based on ASTM recommended test block and the E 2491-06 experimental standard, and the imaging detection results of sectorial scan non-focus method and sectorial scan constant sound path focusing method are provided. Experimental results show that the constant sound path focusing algorithm can effectively detect the defects of the material. Ideal resolution and SNR are achieved to clearly reflect the relative position and the size of the defects in the material.