Ultrasonic phased array (PA) testing is a multi-channel ultrasonic testing (UT) method. Compared with the conventional singular-channel water-immersion ultrasonic testing method, the design of PA testing solution is more flexible and more complex. In the design of a PA testing solution for the structures with complex surface, some mistakes may lead to false detection or missing detection. To design an optimal PA testing solution for structures with complex surface in aerospace, this paper puts forward a design method of PA testing solution and introduces the involved essential techniques and its applications. Firstly, a general overview of the design framework is made to indicate its importance and necessity. Then, the essential techniques of five involved theoretical approaches and their applications are illustrated. Lastly, a PA testing software and hardware platform based on the above techniques is established and applied to the typical structures in aerospace. The results show that the designed PA testing solution can accurately detect the embedded defects within the structure. The proposed design method and the adopted theoretical approaches can improve the design efficiency, and have theoretical significance and a broad application prospect on the detection of complex structures in aerospace and other important fields.