A software-based method called extrapolation method was presented to overcome the trade-off between the sensitivity and the dynamic range of displacement of Shack-Hartmann Wave-front Sensor(HS).Firstly,a beginning focal-spot of a random sub-aperture(A) was obtained,and the focal-spots of the neighbor sub-apertures(B) on A were found through the extrapolation method.By taking a focal-spot of B as the beginning point,the focal-spots of the neighbor sub-apertures on B could be obtained.In the same way,the other focal-spots could also be obtained.In order to demonstrate the feasibility and practicability of the extrapolation method,an experiment was carried out.The results show that the extrapolation method can restore the wave-front while the aberration of the incident wave-front is about twice that of dynamic range of HS,which can satisfy measurement requirements for the large dynamic range and high sensitivity of HS.