The invention relates to a preparation method of potassium sodium niobate ceramic. The preparation method comprises the following steps: grinding a mixture mainly composed of nano KxNa1-xNbO3 powder,a niobium source, a potassium source, a sodium source and a solvent uniformly, pressing the mixture into blocks at a temperature of 150-160 DEG C and a pressure of 430-440 MPa, drying the blocks, andperforming heat treatment above 700 DEG C to obtain the product. In the pressing process of the preparation method, solid phase particles are rearranged, point contact positions among the particles and niobium sources undergo processes of dissolution, reaction and precipitation of potassium sodium niobate amorphous substances in a similar natural ore-forming manner, the precipitated amorphous substances are filled around KxNa1-xNbO3 particles and interstitial positions, internal holes are reduced, the compactness of the material is increased, the amorphous substances are crystallized through later heat treatment, the particles are gradually changed from spherical to polygonal, and finally a densified polycrystalline structure is formed, so that the compactness and piezoelectric performanceof the ceramic are remarkably improved.