Via the method of cold sintering with post-annealing, the lead-free ceramics ${\text{K}}_{0.45}$${\text{Na}}_{0.45}$${\text{Li}}_{0.1}$NbO₃ were prepared. The cold sintered pellet without post-annealing shows a relative density (${\rho }_r)$ of 77.9%, which is larger than ${\rho }_r$ of the green pellet via the conventional solid-state sintering (SSS) method ($～65.1\%$). The cold sintered pellets were post-annealed at temperatures between $975^{°}$C and $1075^{°}$C. The effect of post-annealing temperatures on microstructure, dielectric, ferroelectric and piezoelectric properties of the ceramics was studied in detail. After being post-annealed, the relative densities and grain sizes of the ceramics were increased. The ceramics post-annealed at $1050^{°}$C show excellent dielectric, ferroelectric and piezoelectric properties. Compared to the conventional SSS method, the method of cold sintering with post-annealing is successful in preparing dense ${\text{K}}_{0.45}$${\text{Na}}_{0.45}$${\text{Li}}_{0.1}$NbO₃ lead-free ceramics in a wide temperature range and at relatively low temperatures.