Abstract: The wheels are the key load-bearing parts of the train, and the presence of circumferential and radial cracks on the wheel rims may have an impact on train safety. At present, conventional ultrasonic testing technology is mainly used for detecting the wheels of locomotives in service, which has problems such as a single incident angle and difficulty in receiving reflected echoes from natural cracks. To solve these problems, in this paper, combining existing locomotive flaw detection technology, digital simulation method was used to study the influence of current conventional detection angles on probability of detection (POD) of defects in different directions. Combined with the multi angle scanning characteristics of phased array ultrasonic testing, it showed the role of detection angles in improving defect detection rate in locomotive wheel rim flaw detection. The results showed that phased array ultrasonic testing utilized the advantage of phased array beam deflection and uses multiple angles to cross cover the detection range. Defects with different orientations had good detection effects, and the defect detection rate was higher than that of conventional ultrasonic testing. The advantages of phased array ultrasonic testing mainly lay in its good adaptability to defect direction and high detection rate for small defects.