Ultrasonic imaging technology has advanced rapidly, the escalating demand for imaging quality has driven the continuous development of ultrasonic transducers featuring high-performance. Among them, the crucial factors constraining the further enhancement of imaging quality are the frequency of the device and the intensity of the echo signal. Piezoelectric composites have become a hotspot for ultrasonic transducers and imaging applications due to their excellent properties. However, due to the limitations of the accuracy of the cutting process, the development of piezoelectric/polymer composites is often undermined by undesirable pseudo-vibrations, especially in high-frequency applications, which will significantly reduce energy conversion efficiency. In this study, a novel design method of 1–3 piezoelectric composites with gradient nanoparticle doped polymer is proposed to eliminate the undesired lateral vibrations. Based on the optimized composites, a high-performance composite ultrasonic transducer with a center frequency of 8.51 MHz is prepared. Compared with the traditional composite transducer, the optimized transducer improves the echo voltage amplitude significantly, reaching nearly 3 times. The above advantages are further verified in high-quality ultrasound and photoacoustic imaging. The optimization method has valuable guidance for the design of high-frequency composite transducers, which have great potential in ultrasonic and photoacoustic imaging applications.