In view of industrial applications requiring high piezoelectric activity, KNN-based ceramics face two key constraints: insufficient density and temperature sensitivity. To address these challenges, this study first introduces BaSnO3 and employs two-step sintering method (TSS) for fabrication, thereby synthesizing ternary 0.975K0.5Na0.5NbO3-0.025Bi0.5K0.5TiO3-xBaSnO3 (KNN-1000xBaSn; x=0, 0.3%, 0.6% and 0.9%) with superior piezoelectricity ( =217-257pC/N; =265-330pm/V; =0.16-0.21%), high Curie temperature ( =325-349°C) and densification (4.3-4.5g/cm3; relatively density ∼96%). In one respect, the TSS allows minimal volatilization of alkali metals while promoting grain homogenization. In another respect, the introduction of BaSnO3 enhances the mobility of domain walls, meanwhile fosters diffuse phase transitions (DPT) and widens dielectric peaks without significantly impairing . Moreover, the KNN-6BaSn obtain not only reinforced (256pC/N) with high (325°C) and (1016), but also fatigue resistance and extreme-temperature endurance with excellent (445pm/V at 90°C; 300pm/V at 180°C). This work provides a resultful dual-strategy for the emergence of lead-free piezoelectric products.