Infrared focal plane array detector suffers from problems including the lack of localization technology of infrared devices, intrinsic non-uniformity, low signal-to-noise ratio (SNR). Image acquisition, transmission, and storage cost more and more high for the application of aerospace imaging. To overcome these difficulties, this paper analyzed the principle of computational imaging system, and then the compressive sensing theory was introduced for imaging. Next the imaging prototype was built, and compressed and uncompressed imaging had been experimented. Finally, the method of the signal subspace analysis was introduced for the quality evaluation of reconstructed image, and then the SNR of the reconstructed image was estimated using this method. Experimental results demonstrate that the SNR estimation method is more accurate and effective, and can be as an experimental conclusion that give a reasonable number of samples required for the actual compressed imaging.