Coronagraph is a device used to observe the corona by making a total solar eclipse-like image on the image plane. The dark background of the image plane is provided by the structures used to suppress the stray light in the coronagraph. The structure named Lyot stop is used to remove the diffracted ring formed by diffracted light from the edge of the front aperture. The structure parameters of the Lyot stop are adjusted based on the diffracted light of different wavelengths. The parameters of the Lyot stop are confirmed for removing the diffracted light entirety and enhancing the energy on the image plane radiated by solar corona. The cause of the diffraction rings is analyzed by the simulation of the internally occulting refractive coronagraph. The design and the parameters of the Lyot stop are determined by theoretical analysis. The feature size of the diffracted ring is matched with the parameters of the Lyot stop by the processing of the imaging. The effect of the stray-light suppression based on Lyot stop is achieved by the experiments. The capability of the stray-light suppression of coronagraph is improved.