A nonmydriatic optical system for stereo imaging fundus camera was designed in this work. It could simultaneously capture two images of the same fundus retinal region from different angles, and could enable three-dimensional reconstruction of the fundus. It comprised an imaging system and a lighting system. In the imaging system, the Gullstrand-Le Grand eye model was used to simulate the normal human eye, and the principle of stereomicroscope was employed to design the splitting optical system. In the lighting system, the stray light produced by the retinal objective lens was eliminated using a black dot board, and an annular diaphragm was used to prevent corneal light reflection. Simulation results reveal that the modulation transfer function of each visual field at the cut-off frequency of 95 lp/mm is greater than 0.2, the distortion of the imaging system is less than -3%, and the field curvature is less than 0.1 mm. The stereo imaging system is highly efficient in chromatic aberration correction and focusing, and can provide clear images for the human fundus with the diopters ranging from -10 m-1 to +5 m-1.