In this study, lead-free piezoelectric ceramics, based on the K_0.5Na_0.5NbO_3-xLiNbO₃ (KNN-xLN) system, were fabricated using a conventional method. The influence and mechanism of lithium niobate (LN) doping on the phase structure and temperature-dependent piezoelectric properties of KNN ceramics were meticulously investigated through dielectric temperature spectroscopy and X-ray diffraction (XRD) analysis. Our findings reveal that LN has a solubility limit in KNN of less than 10 mol%. Within this limit, incorporating LN induces a shift in the Curie temperature (T_C) of KNN-xLN ceramics toward higher temperatures, while the transition from orthorhombic to tetragonal phases (T_O-T) is pushed to lower temperatures simultaneously. At room temperature, the ceramics exhibit the coexistence of orthorhombic and tetragonal phases, significantly amplifying their piezoelectric performance. An elevated T_C improves the temperature stability of the ceramics’ piezoelectric properties; specifically, with an LN doping level of approximately 8 mol%, T_C reaches approximately 479 ℃, and the piezoelectric properties of this component ceramic after 470 ℃ heat treatment remain 71% at room temperature. Beyond the solubility threshold, excess LN is prone to forming a secondary phase with potassium, and the residual LN, influenced by its pronounced pyroelectric effect, results in an apparent increase in the d₃₃ coefficient of the ceramics as the heat treatment temperature increases.