Aluminum alloy has become an indispensable part of the automotive industry because of its excellent mechanical properties such as lightweight, high strength, high reliability, maintainability, and low cost. Aluminum alloy is used in automobiles, such as engine blocks, cylinder heads, intake manifolds, brake components, and fuel tanks. Fatigue and fracture are the main reasons for its engineering failure. Surface strengthening techniques, such as ultrasonic shot peening (USP), are often used to improve the fatigue resistance of aluminum alloys. This article expounds on the working principle of USP and elucidates the influence of USP process parameters on the surface characteristics of aluminum alloy. Experimental results observed the effects of USP parameters on surface properties such as surface roughness, microhardness, and surface morphology. The effects of shot peening (SP) diameter, vibration amplitude of ultrasonic vibrating head, and sample placement angle on the surface state of shot-peened materials were studied. Two different shot sizes of 2 mm and 4 mm shot diameter are utilized with two specimen angles at 90° and 0°, having three vibrational amplitudes of 25 μm, 40 μm, and 60 μm for a peening duration of 5 minutes each. The experimental analysis shows that when the SP time is 5 minutes, the surface grain size is significantly refined to the nanoscale. Compared with untreated samples, the surface roughness of treated samples decreases gradually for lower surface coverage. In addition, SP can effectively improve the hardness of the material. In USP treatment, the maximum microhardness increases, and the crack growth rate decreases by increasing the SP diameter and ultrasonic vibration amplitude).