The invention discloses potassium sodium niobate-based leadless piezoelectric ceramic and a preparation method thereof, the chemical formula of the potassium sodium niobate-based piezoelectric ceramic is (1-x) (K0. 5Na0. 5) NbO3-xBi (Li0. 5Sb0. 5) O3, and x is more than or equal to 0.01 and less than or equal to 0.20. The preparation method comprises the following steps: weighing dry raw materials according to a stoichiometric ratio of (1-x) (K0. 5Na0. 5) NbO3-xBi (Li0. 5Sb0. 5) O3, mixing, carrying out ball milling, and drying to obtain a mixed material; pre-sintering the mixed material obtained in the step 1 at a high temperature to obtain pre-sintered powder, and performing secondary ball-milling and drying to obtain secondary ball-milled powder; adding an adhesive into the secondary ball-milled powder, granulating, sieving, and carrying out compression molding, so as to obtain a ceramic blank; removing the organic adhesive, and sintering at high temperature to obtain sintered ceramic; coating the surfaces of the two sides of the sintered ceramic with silver and carrying out high-voltage polarization, and preparing the potassium sodium niobate-based leadless piezoelectric ceramic. Through component design and process optimization, the sintering characteristic of the potassium sodium niobate-based ceramic is effectively improved, volatilization of sodium and potassium elements is inhibited, the porosity is reduced, the density of the ceramic is improved, the dielectric constant is further improved, the loss is reduced, and the comprehensive performance of the KNN-based ceramic is improved.