Silicon thin film on lithium niobate combines the advantages of electronic properties of silicon and optical properties of lithium niobate, making it an ideal platform for high-density integrated optics. In this paper, we present an electro-optic tunable microring resonator in silicon thin film on lithium niobate operating at wavelengths of approximately 1.55 μm. The single-mode conditions, optical power distribution, mode profiles, and propagation losses of silicon waveguides are discussed and compared systematically. Quality factor, free spectral range, and bending losses of silicon microring resonators as different radii for different gap sizes between channel and ring waveguides are analyzed in detail. The bending loss and free spectral range decreased with increasing bending radius while the quality factor increased with increasing radius and gap size. The transmission spectrum of microring with radius R = 10 μm was tuned using the electro-optic effect. The key issues affecting the electro-optic effect, such as silicon film thickness and electric field strength, are discussed. This study is helpful for the understanding of microring structures in silicon thin film on lithium niobate, as well as for the fabrication of high-performance and multifunctional photonic integrated devices.