To satisfy the far ultraviolet space imaging system with super wide field, larger relative aperture, miniaturized size and good stray light suppression, a method based on the inverse focal power allocation theory is applied to calculate the structure of all spherical surface reflective system. The relevant technical parameters of all spherical off- axis optical system include focal length 12 mm, F number 3 and field of view 70° × 10° . Such a design will consider to eliminate stray light of optics and structure, analyze stray light and main sources. The modulation transfer functions (MTF) at the cutoff spatial frequency are larger than 0.7 at all fields and the point sources transmittance (PST) arrives to 4.2 × 107 which is far less than 5 × 105 when the evadable angle out of the field of view is 10° . Compared to other optical systems, the main advantage of this system is that it can achieve super wide field with compact structures, utilizes all spherical mirrors which largely decrease the cost of fabrication, and presents high level of stray light suppression.