The (K0.5Na0.5)NbO3 ceramics, as an important high-performance lead-free piezoelectric material system, are expected to promote the lead-free development of medical ultrasound imaging transducers. The study on the effective doping modification of KNN ceramics was carried out. The KNN-based piezoelectric ceramics with excellent piezoelectric properties were prepared by solid phase sintering method. The piezoelectric constant and the electromechanical coupling coefficient were up to 400 pC/N and 55%, respectively. Based on its high piezoelectricity and low acoustic impedance, a high-resolution and large-bandwidth medical ultrasound transducer with high-resolution and large-bandwidth was prepared. The transducer has an axial resolution of 47 μm, a bandwidth of 93%@-6 dB and a center frequency of 18.0 MHz. Using the prepared transducer to perform B-mode ultrasound imaging on a human tissue model, the high-resolution structure images of tubular tissue have been obtained. The results indicate that the KNN system ceramics are a kind of material with excellent comprehensive performance for medical high-frequency ultrasound imaging.