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