Because of their high toxicity, lead-based materials in electronic devices must be replaced by lead-free piezoelectric materials. However, some issues remain that hinder the industrial applications of these alternative ceramics. Here, we report the construction of a 0-3-type ceramic composite (KNNS-BNKZ: xZnO), where the Sb-doped ZnO sub-micronic particles were randomly distributed throughout the potassium-sodium niobate-based ceramic matrix. In this KNN-based ceramic composite, superior temperature stability, excellent piezoelectric properties, and a high Curie temperature were simultaneously achieved. The unipolar strain varied from +20% to -16% when the temperature was increased from 23 oC to 200 oC in KNNS-BNKZ: xZnO with x=0.75. By increasing the ZnO content from x=0 to 5.0, the Curie temperature was increased from 227 oC to 294 oC. More importantly, the piezoelectric coefficient remained high (d33=480-510 pC/N) for a wide range of compositions, x=0.25-1.0. Transmission electron microscopy (TEM) experiments showed that the compensatory electric fields generated by the Sb-doped ZnO sub-micronic particles were responsible for the improved temperature stability. The high piezoelectricity was due to the existence of nanodomains, which were clearly observed in the TEM experiments. The results presented in this work clarify some of the physical mechanisms in this KNN-based ceramic composite, thus advancing the development of lead-free ceramics.