A compact, high-performance optical system with mechanical compensation was designed with a 30 times continuous zoom for a 640×512-element cooled staring focal plane array detector. The system was designed using the novel three-group zoom in the form and thrice imaging methods. The system operates in the waveband of 3.7~4.8 μm. F/#=4. The zoom ranges from 750 mm to 25 mm. First, gives the schematic drawing of the optical system was obtained with the optical design software. Then, the optical design software has the analysis of the image quality evaluation, the zoom curve analysis, the temperature environment adaptability analysis, and the Narcissus were analyzed with the same software. Finally, the paper proposed a way to improves the resolution of the system using micro-scan imaging technology. The results show that the modulation transfer function ( MTF) of the optical system is close to the diffraction limit at a spatial frequency of 30 lp/mm and the root-mean-square value of its diffusion spot diameter is less than 15 μm. Zoom curve is smooth and the maximum displacement of the move group is less than 71 mm. The focusing and the temperature compensating of the system were achieved via the axially moving of the mobile group lens. The optical system satisfies l00% cold-shield efficiency and has good image quality in the temperature range of -40~ 60 ℃. Meanwhile the optical system meets the requirements of the new generation of airborne forward looking infrared ( FLIR) system.