Optical resonators with high quality (Q) factor can restrict light in a small mode volume for a long time, greatly enhancing the interaction between light and matter, and becoming an important component with great potential in integrated optical devices. Focusing on the silicon nitride material platform, which is currently widely used in the field of integrated nonlinear optics, in order to solve the problem of large scattering loss in the large size on-chip silicon nitride microring resonator caused by the stitching error, the surface roughness and other factors, a series of fabrication process improvements were made to improve the quality factor of the large size silicon nitride microring resonator. The results show that the scattering loss of the silicon nitride waveguide can be effectively reduced by thin film redeposition process, and the intrinsic Q of the large size silicon nitride microring resonator with a radius of 560 μm is increased by 26% on average. Thanks to the improved Q of the large size microring resonator, the frequency comb with the repetition rate of 40 GHz is realized in the on-chip silicon nitride microring resonator.