Because of rotating reflector or refractor,there is nonlinearity of Optical Path Difference(OPD) in high-speed rotary FT-Spectrometer.Nonlinearity which was studied to direct engineering in this paper is a very important aspect to be considered in designing system. In nonlinear OPD system,interferogram is sampled linearly,which brings interferogram phase and period error.The case corresponds to the interferogram without those errors sampled nonlinearly.Interferogram without phase and period errors can be reconstructed with those interferogram data sampled in unequal intervals through fitting polynomial.Then the reconstructed interferogram is sampled in equal intervals.Those data are used to reconstruct spectrum without noise caused by OPD nonlinearity.Computer simulation shows this method is effective,and fits interferogram with quartic polynomial well.The method is also effective in other nonlinear OPD systems.