Under sampling leads to aliasing effect which have seriously effect on the image quality for infrared focal plane arrays. According to the imaging processing of staring system, sampling process of detector was analyzed in the time domain to study aliasing effect on image quality using a quantitative method in the frequency domain. Simulation experiment on aliasing phenomenon of periodic and aperiodic objects based on the reason of aliasing effect was completed. Simulation experiment show that aliasing distortion phenomenon will be exist in periodic objects, but there will be zigzag stripe in aperiodic objects. It can be concluded that aliasing distortion is small in low frequency and noise tends to mask the target pattern, but aliasing distortion is serious in high frequency where aliasing is dominant, this has a certain reference value for eliminating the influence of aliasing confusion and system parameter design.