Since the Fourier transform spectrometer based on multi-micro mirrors samples the interferogram image which corresponds to each OPD in the transverse optical field, the spatial distribution of the irradiance has much effect on the quality of the interferogram. In the present paper, distribution function is introduced in this spectrometer system. By means of simulation, the contrast of the interferogram modulated by distribution function is depressed in the fringe area and the concomitant line appears in the spectrum. According to theory analysis, the decline of the contrast lies on the distribution function which scans the interferogram periodically. And the concomitant line is the effect of the spectrum shift, which belongs to the modulation function. Finally, the difference image and conversed recovery arithmetic are proposed. Via the simulation, the conversed recovery arithmetic can recover the interferogram and the spectrum evidently.