The system of space-modulated Fourier transform infrared spectrometer without moving parts is stable and compact, moreover, it can realize the on-line monitoring and real-time detection. The position accuracy of multi-micromirrors as the key components has a great influence on spectrometric performance. In the present paper, the multi-mcromirrors tilt error caused by optical path difference changes was calculated and simulated. The analysis shows that, as the multi-micromirrors tilt angle increased, the interference pattern contrast decreased and the signal to noise ratio reduced. The results could be used in the tolerance distribution and the systemic alignment in the next step.