High-frequency ultrasonic transducers are essential for high-resolution clinical diagnostics or industrial non-destructive testing. While 1-3 piezoelectric composites offer superior acoustic impedance matching and electromechanical coupling efficiency compared to traditional bulk ceramics, their high-frequency performance is often compromised by periodic lateral vibration modes. These parasitic resonances significantly degrade sensitivity, bandwidth, and imaging quality. To overcome this limitation without increasing manufacturing complexity, this study proposes a gradient-structure piezoelectric composite that uses a non-periodic distribution of piezoelectric pillars to physically disrupts the phase coherence of lateral standing waves. The structural parameters of the piezocomposite were optimized and validated using theoretical derivation and Finite Element Analysis (FEA). Compared to conventional designs, our fabricated high-frequency gradient composite transducer showed significantly improved −6 dB bandwidth (73%), electromechanical coupling coefficient (0.74), and pulse-echo sensitivity. Furthermore, the imaging experiments performed on phantom, tungsten wire and ex vivo tissues indicated that the gradient transducer achieves superior resolution and Contrast-to-Noise Ratio (CNR). These findings indicate that the gradient structure design provides a practical solution to current performance bottlenecks of high-frequency transducers, offering substantial theoretical significance and broad application potential in precision medical ultrasound imaging.