In the technology of wavefront coding, a special phase mask is put at the position of optical system stop. Then the goal signal wavefront will be coded. At the image processing part, the coded signal will be decoded to the original image. Because the insensitivity of the coded wavefront to the defocus and other aberrations is ten times more, the focus depth will be extended ten times more. So the wavefront coding can solve the defocus and alignment error caused by terrible mechanics and heat environment using coding and decoding. Based on the extended focus depth principle of wavefront coding, an aberration inactivation long/long double bands infrared optical system was designed. The focus depth was extended to be 10 times more. Imaging test was carried out with the wavefront coding prototype. The coding image of the spot-bar was used as the PSF to decode the image at the 10 times defocus position of cross-bar and four-bar. After decoding, the image of cross-bar and four-bar was with high resolution. At the last, the imaging results of wavefront coding were analyzed. The ripple of decoding picture was caused by not enough spatial sampling. After sampling PSF of different field, the ripple could be eliminated by using decoding algorithm of spatial transformation. The signal and noise would be extended at same time while the image was decoding. So the noise suppression algorithm used in decoding should be further researched to satisfy the missile-borne demand of more energy and higher signal to noise ratio.