An optimization method for designing a light-weight point mirror for a space camera is proposed. The light-weight design of a point mirror with a size of 360 mm×560 mm for a space camera is carried out. It is optimized by taking the mirror thickness, tip angle, face-sheet thickness, and rib-sheet thickness as design variables, by taking the minimum weight as the design objective, by using the figure peak value less than 55 nm and the root-mean-square value less than 11 nm as restraint conditions and by reducing the weight of the whole mirror from 4 kg to 1.72 kg (its face density is 8.0 kg/m2). Then, taking the minimum figure under the condition of microgravity as the objective, the supporting points of the designed light-weight mirror are optimized. The resulting figure peak value is 54 nm. The deformation and modality of the mirror under the condition of microgravity, rotation inertia and temperature change are calculated and verified by using a finite-element analysis method. All of the results meet the requirements for space application. Finally, the effect of the deformation due to the synthetic action of the space environment on the image quality of the optical system is analyzed by using an opto-mechanical-thermal integrated simulation method. The result shows that because of the deformation of the pointing mirror, the modulated transfer function of the optical remote sensing system is reduced from 0.735 to 0.703 with a reduction ratio of 4.4%, which meets the design requirement.