The invention discloses a two-stage space optical coupling device capable of improving the space optical coupling efficiency of a single-mode optical fiber, and belongs to the technical field of freespace optical communication. The prior art coupling is inefficient. Primary converging lens, multimode optical fibers, large numerical aperture variable refractive index lens and small numerical aperture variable refractive index lens are sequentially coaxially arranged along the light incident direction; the numerical apertures of the primary converging lens, the multimode optical fibers and thelarge numerical aperture variable refractive index lens are equal or are increased in sequence; the incident end face of the multimode optical fibers is positioned at the focal point of the image sideof the primary converging lens, and the emergent end face is positioned at the focal point of the large numerical aperture variable refractive index lens; the emergent mirror surface of the large numerical aperture variable refractive index lens is abutted against the incident mirror surface of the small numerical aperture variable refractive index lens; the refractive index decreasing rate of the large numerical aperture variable refractive index lens is higher than the refractive index decreasing rate of the small numerical aperture variable refractive index lens; the outer diameters of themultimode ferrule of the multimode optical fibers, the large numerical aperture variable refractive index lens and the small numerical aperture variable refractive index lens are the same, and the multimode ferrule of the multimode optical fibers, the large numerical aperture variable refractive index lens and the small numerical aperture variable refractive index lens are in static fit with theinner wall of the sleeve.