Abstract: High imaging quality is required in the small-aperture high-resolution space-to-ground remote sensor of refractive system，as a result the assemblage tolerance is rigorous. The assemblage tolerance distribution rooted in optics design before, however, the strict tolerance cannot be achieved in smallaperture high-resolution space remote sensor now. An improved tolerance distribution was recommended based on the combination of optic design and assembly practice.It estimated the imaging quality through the emulation of whole process, reallocated the tolerance and adjusted it by compensation realtimely . The improved tolerance distribution was proved by a small-aperture camera lens assemblage.Results show that the control accuracy of eccentric error is 2,and that of mirror spacing is 1 m,the imaging quality is good after camera assemblage.