We investigated the microstructures and the electrical properties of $ZrO_2$thin films deposited by reactive DC magnetron sputtering on (100) Si with different deposition conditions and annealing treatments. The refractive index of the $ZrO_2$ thin films increased with annealing temperatures and deposition powers, and approached to the ideal value of 2.0~2.2. The $ZrO_2$thin films deposited at the room temperature are amorphous, and the films are polycrystalline at the deposition temperature of $300^{circ}C$. Both the thickness of the interfacial oxide layer and the root-mean-square (RMS) value of surface roughness increased upon annealing in the oxygen ambient. The Cmax value and leakage current value decreased with the increase of thickness of the interfacial oxide thickness.