A resonance structure of bulk acoustic wave resonator comprises a bottom electrode, a dielectric layer and a top electrode, wherein the dielectric layer is formed on the bottom electrode; the top electrode is formed on the dielectric layer. A resonance area is defined by the overlapping area of the projection of the bottom electrode, the dielectric layer and the top electrode. The resonance area has a contour. The contour includes at least three curved edges and is formed by connecting the at least three curved edges. Each curved edge is concave to a geometric center of the contour.