Terahertz (THz) wave has a potential application prospect in the field of space observation because of its high transmittance and spatial and temporal resolution. Large field-of-view imaging is required for staring optical systems, and compared to scanning imaging, staring imaging has the advantages of high imaging performance, quick speed, and simple structure. As a result, the design of a large field-of-view staring THz optical system has important engineering application value. Zemax and an inverse telephoto structure are used to create a large field-of-view THz optical imaging system with a relative aperture of 1 and a full field-of-view angle of 60°. The system adopts a 4-piece reverse-telephoto coaxial structure, consisting of 2 spherical lenses and 2 aspherical lenses, and the lens material is polymethylpentene (TPX) material. Compactness and lightweight are advantages of the entire system. The modulation transfer function (MTF) value of the full field-of-view at the spatial frequency of 12.5 lp/mm is higher than 0.3, and the optimization results demonstrate that the root mean square radius of the diffuse spot in each field-of-view is smaller than the Airy spot radius, demonstrating the system's high imaging quality. Additionally, the system's robustness is demonstrated by the results of the tolerance analysis, and it is simple to reach the required processing technology level. This design has significant reference value for THz space large field-of-view high-resolution detection.