It is found that space optical sensor is influenced negligibly by atmosphere turbulence when targeting the ground, which
makes primary mirror figure deformation caused by gravity t variation and temperature become a part of main reasons
for resolution degration. At present, a reference wavefront is used to detect the primary mirror figure deformation. In the
choice of a proper reference light source, many aspects must be considered, such as environment, size, energy
consumption, signal to noise ratio,etc.. The reference source method available can't satisfy the demands mentioned
above. As a result, a new approach for detecting primary mirror figure deformation of space optical remote sensor is put
forward, namely, the beacon is embedded in the system, and some sampling mirrors are located in the primary mirror.
Then we can get light spot location variation of every sampling mirror when the primary mirror figure deformation
occur, and figure out deformation distribution by modal reconstruction. From simulation, it is found that this approach
can recover primary mirror figure deformation with RMS error less than λ/30, when the peak-valley value of figure
deformation is around 1 λ .